Semiconductor device

ABSTRACT

A driver IC (Integrated Circuit) includes a power supply terminal; an output terminal to be coupled to a load element; a connection node on a current path between the power supply terminal and the output terminal; a substrate resistance, having one end coupled to the connection node; an output transistor including a gate, wherein the output transistor is coupled in series with the substrate resistance through the connection node; a resistance, having one end coupled to an other end of the substrate resistance; and a voltage detecting circuit configured to detect a voltage depending on a voltage between the one end of the substrate resistance and the other end of the substrate resistance, and to output an output signal, which is as an output of the voltage detecting circuit, to the gate of the output transistor.

CROSS-REFERENCE

The present application is a Continuation application of U.S. patent application Ser. No. 14/808,503, filed on Jul. 24, 2015, which is a Continuation application of U.S. patent application Ser. No. 14/307,674, now U.S. Pat. No. 9,153,688 B2, issued on Oct. 6, 2015, which is based on Japanese Patent Application No. 2013-144380 filed on Jul. 10, 2013, and Japanese Patent Application No. 2014-074628, filed on Mar. 31, 2014, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention is related to a semiconductor device, and especially to a semiconductor device configured to drive a load by using a power transistor.

BACKGROUND ART

In a semiconductor device which drives a load by using a power transistor, there is a case where a detection function is implemented to detect the state of the load. As the detection of the state of the load, the detection of a load extraordinary state is exemplified (such as over-current, a light load state (a disconnected state of a part of the load), no load state (a fully disconnected state of the load), and the detection of the load current which flows through the load.

Various techniques are proposed to detect a load current precisely. For example, Patent Literature 1 (JP H10-116917A) discloses a technique of detecting the output current of a planar-type bipolar transistor. This Patent Literature discloses a structure that an electrode is provided in an exposed collector layer on the surface of a transistor chip to take out a voltage drop due to the resistance of a silicon substrate as a current detection signal.

Also, the current according to the output transistor provides a transistor for the flowing sense and Patent Literature 2 (JP 2011-166518A) discloses a technique that a current which flows through a sense transistor according to an output transistor is detected as a voltage drop due to a sense resistance. Moreover, Patent Literature 3 (JP H08-102649A) discloses a technique that a current which flows through a sense MOS transistor according to a power MOS transistor used as an output transistor is detected by a current detecting circuit which is connected with a source of the sense MOS transistor. In the technique disclosed in the Patent Literature 3, a source-drain voltage of the power MOS transistor and a source-gate voltage of the sense MOS transistor are adjusted to be same by a voltage source connected between the source of the power MOS transistor and the minimum voltage point of the current detecting circuit.

CITATION LIST

-   -   [Patent Literature 1] JP H10-116917A     -   [Patent Literature 2] JP 2011-166518A     -   [Patent Literature 3] JP H08-102649A

SUMMARY OF THE INVENTION

However, according to the consideration by the inventor, in these prior arts, there are points to be improved in the detection precision of the state of the load.

Other problems and new features would be made clear from the description of Specification and the attached drawings.

In one embodiment, a semiconductor device includes a first semiconductor region of a first conductive type, a common drain electrode, second and third semiconductor regions of a second conductive type which is different from the first conductive type, first and second diffusion layers of the first conductive type, and a gate electrode. The common drain electrode is electrically connected with the first semiconductor region. The second semiconductor region is joined to the first semiconductor region and the first diffusion layer is formed in the second semiconductor region. The first diffusion layer functions as a source of a first transistor. The third semiconductor region is joined to the first semiconductor region and the second diffusion layer is formed in the third semiconductor region. The second diffusion layer functions as a source of a second transistor. The gate electrode is provided to oppose to the first semiconductor region, the second semiconductor region and the third semiconductor region through a gate insulating film. A load current flows between the common drain electrode and the first diffusion layer. The voltage of the second diffusion layer (that is, the source of the second transistor) is used for the detection of the load state.

In an example of the above embodiment, it is possible to improve the detection precision of the state of the load. In another example of the above embodiment, it is possible to improve the detection precision of the load current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a configuration of a semiconductor device according to a first embodiment.

FIG. 2A is a diagram schematically showing an example of the configuration of a comparator.

FIG. 2B is a diagram schematically showing another example of the configuration of the comparator.

FIG. 2C is a diagram schematically showing another example of the configuration of the comparator.

FIG. 3 is a sectional view showing the structure of an output device section and a control circuit section in the first embodiment.

FIG. 4 is a sectional view showing the structure of the output device section and the control circuit section in the first embodiment.

FIG. 5 is a plan view showing the structure of the semiconductor device in the first embodiment.

FIG. 6 is a conceptual diagram showing a current path when a load current flows through an output MOS transistor, in the first embodiment.

FIG. 7 is an expanded view showing a sectional structure of the output MOS transistor and a sense MOS transistor.

FIG. 8A is a diagram schematically showing an equivalent circuit of the electrical connection between a load terminal, a node n1 and a back electrode 33.

FIG. 8B is a diagram showing current which flows inside the semiconductor device of the first embodiment and a voltage distribution inside the semiconductor device.

FIG. 9 is a diagram schematically showing a modification example of the configuration of the semiconductor device in the first embodiment.

FIG. 10 is a sectional view showing another example of the structure of the output MOS transistor and the sense MOS transistor.

FIG. 11 is a sectional view of another example of the structure of the output MOS transistor and the sense MOS transistor.

FIG. 12 is a sectional view of another example of the structure of the output MOS transistor and the sense MOS transistor.

FIG. 13 is a sectional view showing a path through which the load current flows in the output MOS transistor of the structure of FIG. 12.

FIG. 14 is a sectional view showing the structure when an output IGBT and a sense IGBT are used instead of the output MOS transistor and the sense MOS transistor in the semiconductor device of the first embodiment.

FIG. 15 is a sectional view showing a path through which the load current flows in the output IGBT of the structure of FIG. 14.

FIG. 16 is a sectional view showing another structure of the output device section in the first embodiment.

FIG. 17 is a sectional view showing another structure of the output device section in the first embodiment.

FIG. 18 is a diagram schematically showing the configuration of the semiconductor device in a second embodiment.

FIG. 19 is a sectional view showing the structure of the output device section and the control circuit section in the second embodiment.

FIG. 20 is a sectional view showing the configuration of the semiconductor device in a third embodiment.

FIG. 21 is a plan view showing the configuration of the semiconductor device in the third embodiment.

FIG. 22 is a sectional view showing a modification example of the configuration of the semiconductor device in the third embodiment.

FIG. 23 is a plan view showing the configuration of the semiconductor device of FIG. 22.

FIG. 24 is a diagram schematically showing the configuration of the semiconductor device in a fourth embodiment.

FIG. 25 is a sectional view showing the structure of the output device section and the control circuit section in the fourth embodiment.

FIG. 26 is a sectional view showing a path through which the load current and the sense current flow in the output device section of the fourth embodiment.

FIG. 27 is a diagram schematically showing a modification example of the configuration of the semiconductor device of the fourth embodiment.

FIG. 28 is a sectional view showing the structure of the output device section and the control circuit section in the semiconductor device of FIG. 27.

FIG. 29 is a conceptual diagram showing an example of an in-vehicle electronic system installed in a vehicle and applied with the semiconductor device of the first to fourth embodiment.

FIG. 30 is a block diagram showing an example of the configuration of an electronic control unit to which the semiconductor device of the first to fourth embodiments is applied.

FIG. 31 is a block diagram showing a connection between a MCU and a driver IC when the semiconductor chip shown in FIG. 1 is used as the driver IC of the electronic control unit.

FIG. 32 is a flow chart showing an example of the operation of the MCU when the configuration of FIG. 31 is adopted.

FIG. 33 is a block diagram showing a connection between the MCU and the driver IC when the semiconductor chip shown in FIG. 9 is used as the driver IC of the electronic control unit.

FIG. 34 is a flow chart showing an example of the operation of the MCU when the configuration of FIG. 33 is adopted.

FIG. 35 is a block diagram showing a connection between the MCU and the driver IC when the semiconductor chip shown in FIG. 18 is used as the driver IC of the electronic control unit.

FIG. 36 is a block diagram showing a connection between the MCU and the driver IC when the semiconductor chip shown in FIG. 24 is used as the driver IC of the electronic control unit.

FIG. 37 is a flow chart showing an example of the operation of the MCU when the configuration of FIG. 36 is adopted.

FIG. 38 is a block diagram showing a connection between the MCU and the driver IC when the semiconductor chip shown in FIG. 27 is used as the driver IC of the electronic control unit.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

FIG. 1 is a diagram schematically showing a configuration of a semiconductor device according to a first embodiment. As shown in FIG. 1, the semiconductor device in the first embodiment has a semiconductor chip 1 which functions as a high side driver IC (integrated circuit) disposed between a DC power supply 2 and a load 3. The semiconductor chip 1 receives supply of a power supply voltage V_(CC) from the DC power supply 2 and has a function of switching the supply of the DC power supply voltage V_(CC) to the load 3. For example, as the DC power supply 2, a battery is used.

The semiconductor chip 1 has a control input terminal 11, a power supply terminal 12, a load terminal 13, an output device section (SEC.) 14 and a control circuit section (SEC.) 15. That is, the control input terminal 11, the power supply terminal 12, the load terminal 13, the output device section 14 and the control circuit section 15 are integrated monolithically on the semiconductor chip 1. Here, the term “monolithically” means that they are integrated on the identical semiconductor chip. The control input terminal 11 is an external connection terminal which receives an external control signal IN from an external unit (e.g. CPU (central processing unit)). The power supply terminal 12 is an external connection terminal which is connected with the DC power supply 2, and receives the power supply voltage V_(CC) supplied from the DC power supply 2. The load terminal 13 is a terminal which is connected with the load 3.

An output MOS transistor (Tr.) 21 and a sense MOS transistor (Tr.) 22 are integrated in the output device section 14 as power transistors for switching the supply of the power supply voltage V_(CC) to the load 3. In the present embodiment, the output MOS transistor 21 and the sense MOS transistor 22 are both formed as NMOS transistors having a UMOS (U-groove MOS) structure. The output MOS transistor 21 and the sense MOS transistor 22 have drains connected in common (a common drain), and the common drain is connected with the power supply terminal 12. A source of the output MOS transistor 21 is connected with the load terminal 13 and a source of the sense MOS transistor 22 is connected with a node n1. The load current I_(OUT) is supplied to the load 3 from the DC power supply 2 through the output MOS transistor 21.

Here, in FIG. 1, a symbol R_(SUB) shows a substrate resistance. The substrate resistance R_(SUB) can be expressed as a resistance in the common drain of the output MOS transistor 21 and the sense MOS transistor 22 in an equivalent circuit. Note that the output MOS transistor 21 and the sense MOS transistor 22 are shown as different devices in the equivalent circuit diagram of FIG. 1. However, the output MOS transistor 21 and the sense MOS transistor 22 are formed as a physically unitary body, to be mentioned later. The node n1 is connected with the source of the sense MOS transistor 22 and is used to detect a voltage drop due to the substrate resistance R_(SUB), to be mentioned later.

The control circuit section 15 has a node n2 and has a control circuit block 23 and a voltage detecting circuit 24. As mentioned later, the node n2 is a node having a voltage corresponding to the voltage of a common drain electrode (an electrode connected with the common drain) of the output MOS transistor 21 and the sense MOS transistor 22. The take-out of a voltage to the node n2 will be described later in detail.

The control circuit block 23 has a logic circuit 25 and a charge pump 26. The logic circuit 25 generates a control signal S_(CTRL) for controlling the charge pump 26 in response to the external control signal IN and a detection signal S_(DET) outputted from the voltage detecting circuit 24. The control signal S_(CTRL) supplied to the charge pump 26 is a signal to control the drive of the gates of the output MOS transistor 21 and the sense MOS transistor 22 by the charge pump 26. That is, the logic circuit 25 has a function of controlling the drive of the gates of the output MOS transistor 21 and the sense MOS transistor 22 by the charge pump 26 in response to the external control signal IN and the detection signal S_(DET).

The charge pump 26 operates as a drive circuit for driving the gates of the output MOS transistor 21 and the sense MOS transistor 22 in response to the control signal S_(CTRL) which is supplied from the logic circuit 25, and generates a gate voltage V_(G) which should be supplied to the gates of the output MOS transistor 21 and the sense MOS transistor 22. The charge pump 26 is configured in such a manner that it can generate the gate voltage V_(G) which is higher than the DC power supply voltage V_(CC) (for example, the gate voltage V_(G) of about twice of the DC power supply voltage V_(CC)). In the present embodiment, when the control signal S_(CTRL) is in a high level, the charge pump 26 supplies the gate voltage V_(G) of about twice of the DC power supply voltage V_(CC) to the gates of the output MOS transistor 21 and the sense MOS transistor 22. When the control signal S_(CTRL) is in a low level, it stops the drive of the gates of the output MOS transistor 21 and the sense MOS transistor 22.

The control circuit block 23 may contain circuits other than the logic circuit 25 and the charge pump 26, e.g. a short-circuit which connects the source and the gate in the output MOS transistor 21, and an abnormal detecting circuit and so on.

The voltage detecting circuit 24 is a circuit section which generates the detection signal S_(DET) based on a voltage (a voltage difference) between the node n1 connected with the source of the sense MOS transistor 22 and the node n2. As described later in detail, the voltage between the node n1 and the node n2 corresponds to the current level of the load current I_(OUT), and therefore, the voltage detecting circuit 24 has a function of detecting the current level of the load current I_(OUT) as a voltage. The voltage detecting circuit 24 has a set threshold voltage generating section 27 and a comparator 28.

The set threshold voltage generating section 27 has a voltage source which generates a desired set threshold voltage V_(TH). The set threshold voltage generating section 27 is connected with the node n2 on its higher voltage side and connected with the + input terminal (a non-inversion input) of the comparator 28 on its lower voltage side. That is, the + input terminal of the comparator 28 is set to a voltage which is lower than the voltage of the node n2 by the threshold voltage V_(TH) through the operation of the set threshold voltage generating section 27.

The comparator 28 compares the voltage at the + input terminal and the voltage at the − input terminal (inversion input) to generate the detection signal S_(DET) corresponding to the comparison result. In the present embodiment, the comparator 28 sets the detection signal S_(DET) to the high level when the voltage at the + input terminal is higher than the voltage at the − input terminal, and sets the detection signal S_(DET) to the low level in the other case. As a result, the detection signal S_(DET) is in the high level when the voltage difference ΔV21 (=Vn2−Vn1) between the voltage Vn1 at the node n1 and the voltage Vn2 at the node n2 is greater than the set threshold voltage V_(TH), and is in the low level in the other case.

FIG. 2A to FIG. 2C are diagrams schematically showing an example of the circuit configuration of the comparator 28.

In one example, the comparator 28 has a pair of MOS transistors as an input transistor pair. In this case, the gates of the MOS transistors may be used as the + input terminal and the − input terminal. FIG. 2A shows an example of the configuration of such a comparator 28.

In the configuration of FIG. 2A, the comparator 28 has PMOS transistors (P-channel MOS transistors) MP11 and MP12, and NMOS transistors (N-channel MOS transistors) MN11, MN12 and MN13 and constant current sources 101 and 102.

Sources of the PMOS transistors MP11 and MP12 are connected with one end of the constant current source 101 in common and gates thereof are respectively used as the − input terminal and the + input terminal in the comparator 28. The other end of the constant current source 101 is connected with a power supply line 103 to which the DC power supply voltage V_(DD) is supplied. Here, the DC power supply voltage V_(DD) is a voltage which is generated from the DC power supply voltage V_(CC) supplied to the power supply terminal 12. The constant current source 101 supplies the constant current to an input transistor pair consisting of the PMOS transistors MP11 and MP12.

Drains of the NMOS transistors MN11 and MN12 are connected with the drains of the PMOS transistors MP11 and MP12, respectively, and the gates thereof are connected to the drain of the NMOS transistor MN11 in common and the sources thereof are connected to a power supply line 104 having a ground voltage GND, in common.

A drain of the NMOS transistor MN13 is connected with an output terminal of the comparator 28, a source thereof is connected with the power supply line 104, and a gate thereof is connected with the drain of the NMOS transistor MN12. The constant current source 102 is connected between the output terminal and the power supply line 103 and supplies a constant current to the NMOS transistor MN13.

In such a configuration, because the gates of the PMOS transistors MP11 and MP12 are used as the − input terminal and the + input terminal in the comparator 28, the input current is substantially zero.

Note that in FIG. 2A, the PMOS transistors MP11 and MP12 are used as the input transistor pair. However, the NMOS transistors may be used as the input transistor pair. In this case, the conductive type of each MOS transistor is reversed, and also the DC power supply voltage V_(DD) is supplied to the power supply line 104 and the power supply line 103 is set to the ground voltage GND.

Also, as shown in FIG. 2B, instead of the PMOS transistors MP11 and MP12, PNP-type bipolar transistors TR11 and TR12 may be used. In this case, emitters of the bipolar transistors TR11 and TR12 are connected to the constant current source 101 in common and collectors thereof are connected with the drains of the NMOS transistors MN11 and MN12, respectively. Moreover, bases of the bipolar transistors TR11 and TR12 are used as the − input terminal and the + input terminal in the comparator 28, respectively.

In such a configuration, a minute input current flows through the comparator 28.

Specifically, when the current supplied from the constant current source 101 to the bipolar transistors TR11 and TR12 is 5 μA and the DC amplification factors h_(FE) of the bipolar transistors TR11 and TR12 are 50, the input current is 0.1 μA.

In FIG. 2B, the PNP-type bipolar transistors TR11 and TR12 are used as the input transistor pair. However, NPN-type bipolar transistors can be used as the input transistor pair. In this case, the conductive type of each transistor is reversed, and also the DC power supply voltage V_(DD) is supplied to the power supply line 104, and the power supply line 103 is set to the ground voltage GND.

FIG. 2C shows an example of another configuration of the comparator 28. In the configuration of FIG. 2C, the comparator 28 has PMOS transistors MP13 and MP14 and constant current sources 105 and 106. Drains of the PMOS transistors MP13 and MP14 are connected with one ends of the constant current sources 105 and 106, respectively, and gates thereof are connected to the drain of PMOS transistor MP13 in common. The other ends of the constant current sources 105 and 106 are connected with a ground line 107 which has the ground voltage GND. Sources of the PMOS transistors MP13 and MP14 are used as the − input terminal and the + input terminal in the comparator 28, respectively, and the drain of the PMOS transistor MP14 is used as an output terminal.

Here, in any case of the circuit configurations of FIG. 2A to FIG. 2C, the detection signal S_(DET) which is outputted from the comparator 28 depends on the voltages of the + input terminal and the − input terminal. However, note that the input current of the comparator 28 is kept at a constant value (except for the influence of undesired phenomena such as a change of the DC power supply voltage). In this meaning, the comparator 28 (or the voltage detecting circuit 24 having the set threshold voltage generating section 27 and the comparator 28) is a circuit which detects voltage.

FIG. 3 is a cross-sectional view showing a structure of the semiconductor chip 1 in which the circuit of FIG. 1 is integrated, especially, the structure of the output MOS transistor 21 and the sense MOS transistor 22. The semiconductor chip 1 has a semiconductor substrate 30. The semiconductor substrate 30 has an N⁺ substrate 31 and an N-type semiconductor region 32 formed on a front-side main surface 31 a of the N⁺ substrate 31. The N⁺ substrate 31 is an N-type (impurity heavily doped) semiconductor substrate in which an N-type impurity is heavily doped (the semiconductor substrate of a first conductive type). That is, the N⁺ substrate 31 has a semiconductor region in which the N-type impurity is heavily doped (impurity for the first conductive type). Here, the phrase of “heavily doped” in this Specification means that the impurity is heavily doped to an extent that a degenerated semiconductor is formed. The N-type impurity has been doped in the N-type semiconductor region 32 to form an N-type semiconductor region (the semiconductor region of the first conductive type).

A back electrode 33 is formed on a back-side main surface of semiconductor substrate 30, i.e. the back-side main surface 31 b of the N⁺ substrate 31, and this back electrode 33 is connected with the power supply terminal 12 to which the DC power supply voltage V_(CC) is supplied. The N⁺ substrate 31 functions as a common drain of the output MOS transistor 21 and the sense MOS transistor 22 and the back electrode 33 functions as a common drain electrode electrically connected with the common drain.

The output MOS transistor 21 and the sense MOS transistor 22 are formed in the output device section 14. In detail, the semiconductor substrate 30 has P-type base regions (body regions) 34 and 35 which are formed in the N-type semiconductor region 32 in the output device section 14, and the N⁺ diffusion layers 36 and 37 are formed in the P-type base regions 34 and 35. The P-type base regions 34 and 35 are semiconductor regions into which the P-type impurity (a second conductive type of impurity) is doped (that is, the semiconductor regions of the second conductive type). Also, the N⁺ diffusion layers 36 and 37 are semiconductor regions in which the N-type of impurity is heavily doped. The P-type base region 34 is a region where a channel of the output MOS transistor 21 is formed and the P-type base region 35 is a region where a channel of the sense MOS transistor 22 is formed. Also, the N⁺ diffusion layer 36 functions as a source of the output MOS transistor 21 and the N⁺ diffusion layer 37 functions as a source of the sense MOS transistor 22. The N⁺ diffusion layers 36 and 37 are provided to be contact with the front-side main surface 30 a of the semiconductor substrate 30.

Moreover, a source electrode 38 is formed to be joined with the N⁺ diffusion layer 36, and a source electrode 39 is formed to be joined with the N⁺ diffusion layer 37. That is, the source electrode 38 is electrically connected with the source of the output MOS transistor 21, and the source electrode 39 is electrically connected with the source of the sense MOS transistor 22. The source electrode 38 is connected with the load terminal 13 and the source electrode 39 is connected with the node n1. As mentioning above, note that the node n1 is connected with one of the input terminals of the comparator 28 (− input terminal) for a voltage detection.

For example, in the manufacturing process of the semiconductor chip of the present embodiment, the N-type semiconductor region 32, the P-type base regions 34 and 35 and the N⁺ diffusion layers 36 and 37 can be formed as follows. The N-type semiconductor layer is epitaxially grown on the front-side main surface 31 a of the N⁺ substrate 31 as an N-type epitaxial layer. The P-type base regions 34 and 35 are formed by implanting P-type impurity into the surface section of the N-type epitaxial layer and the N⁺ diffusion layers 36 and 37 are formed by implanting the N-type impurity into the surface section of the P-type base regions 34 and 35. A region of the N-type epitaxial layer where the P-type base regions 34 and 35 and the N⁺ diffusion layers 36 and 37 are not formed is used as the N-type semiconductor region 32.

Moreover, trenches (ditches) are formed in the semiconductor substrate 30 to pass through regions between the P-type base regions 34 and 35 to the N-type semiconductor region 32, and a gate insulating film 40 is formed to cover the side surface and the base surface of each trench. Moreover, a gate electrode 41 is formed on the gate insulating film 40 to embed the trench.

The gate electrodes 41 is formed to oppose to the P-type base region 34 or 35 through the gate insulating film 40 in the side surface and to oppose to the N-type semiconductor region 32 through the gate insulating film 40 in the base surface. When a positive voltage which exceeds the threshold voltages of the output MOS transistor 21 and the sense MOS transistor 22 is applied to the gate electrode 41, an inversion layer is formed on the surface of the P-type base region 34 or 35 which opposes to the gate electrode 41, and an accumulation layer is formed on the surface of the N-type semiconductor region 32 which opposes to the gate electrode 41. The inversion layer which is formed on the surface of the P-type base region 34 opposing to the gate electrode 41 is used as a channel of the output MOS transistor 21. The inversion layer which is formed on the surface of the P-type base region 35 opposing to the gate electrode 41 is used as a channel of the sense MOS transistor 22.

In the configuration of FIG. 3, the plurality of gate electrodes 41 are formed and the plurality of gate electrodes 41 are electrically connected. The gate electrodes 41 are used as the common gate of the output MOS transistor 21 and the sense MOS transistor 22. The gate voltage V_(G) is supplied to the gate electrode 41 from the charge pump 26. Note that the gate electrodes 41 may be physically formed as one conductor. For example, the gate electrodes 41 may be formed like meshes in case of plane layout.

On the other hand, in the control circuit section 15, circuit devices (specifically, devices such as an NMOS transistor, a PMOS transistor, and a capacitor) (not illustrated) are formed in the surface section (that is, a surface section of the N-type semiconductor region 32) of the semiconductor substrate 30. Each of the control circuit block 23 and the voltage detecting circuit 24 is formed by using those circuit devices.

In addition, a configuration to take out the voltage of the common drain electrode of the output MOS transistor 21 and the sense MOS transistor 22, i.e. the voltage of the back electrode 33 is provided for the control circuit section 15. In detail, an N⁺ diffusion layer 42 is formed in the surface section of the N-type semiconductor region 32, and a voltage taking-out electrode 43 is formed on the N⁺ diffusion layer 42. The N-type impurity is heavily doped into the N⁺ diffusion layer 42. The voltage taking-out electrode 43 is connected with the node n2. As mentioned above, the node n2 is a node which is connected with the terminal on the higher voltage side of the set threshold voltage generating section 27.

Note that FIG. 3 shows the plurality of the source electrodes 38 which are formed and electrically connected to each other. However, the source electrode 38 may be physically formed as one unit. FIG. 4 is a sectional view showing the structure of the semiconductor chip 1 when the source electrode 38 is formed physically as one unit. An interlayer insulating film 44 is formed to cover the front-side main surface 30 a of the semiconductor substrate 30, and openings are formed to pass through the interlayer insulating film 44 to the N⁺ diffusion layer 36. The source electrode 38 is connected with the N⁺ diffusion layer 36 through the opening. Also, an opening is formed to pass through the interlayer insulating film 44 to the N⁺ diffusion layer 37, and the source electrode 39 is connected with the N⁺ diffusion layer 37 through the opening. Moreover, an opening is formed to pass through the interlayer insulating film 44 to the N⁺ diffusion layer 42, and the voltage taking-out electrode 43 is connected with the N⁺ diffusion layer 42 through the opening. Note that the source electrodes 38 on the right side and the source electrode 38 on the left side are separated from each other in FIG. 4. However, actually, they are connected a position other than the section shown in FIG. 4 (hereinafter, refer to FIG. 5).

FIG. 5 is a diagram showing an example of the planar layout of the semiconductor chip 1. For the purpose of the increase of driving ability, an almost part of the output device section 14 is occupied by the output MOS transistor 21. In detail, the source electrode 38 of the output MOS transistor 21 is formed on the almost part of the output device section 14 and a minute notch section is provided in the source electrode 38. The source electrode 39 of the sense MOS transistor 22 is provided in the notch section. The source electrode 39 is connected with the − input terminal of the comparator 28 by the node n1. A ring wiring line 56 is provided in the peripheral section of the output device section 14 to surround the source electrode 38, and the gate electrode 41 of the output MOS transistor 21 is connected with the ring wiring line 56 (the gate electrode 41 is not shown in FIG. 5). The output of the charge pump 26 of the control circuit block 23 is connected with the ring wiring line 56 through an output gate wiring line 55. Also, the source electrode 38 is connected with the control circuit block 23 through an output source wiring line 57.

On the other hand, the above-mentioned voltage taking-out electrode 43 is provided for the control circuit section 15, and the voltage taking-out electrode 43 is connected with the terminal of the set threshold voltage generating section 27 on the higher voltage side by the node n2. The terminal of the set threshold voltage generating section 27 on the lower voltage side is connected with the + input terminal of the comparator 28.

Next, the operation of the semiconductor device in the present embodiment will be described.

Referring to FIG. 1, the external control signal IN is supposed to have been set to the low level in the initial state. In this case, the control signal S_(CTRL) is set to the low level by the logic circuit 25, and the charge pump 26 does not drive the gate electrodes 41 of the output MOS transistor 21 and the sense MOS transistor 22. Therefore, the output MOS transistor 21 and the sense MOS transistor 22 are both turned off so that the load current I_(OUT) does not flow.

When the external control signal IN is set to the high level, the logic circuit 25 sets the control signal S_(CTRL) to the high level. When the control signal S_(CTRL) is set to the high level, the charge pump 26 supplies the gate voltage V_(G) which is higher than the DC power supply voltage V_(CC) (for example, about twice of the DC power supply voltage V_(CC)) to the gate electrodes 41 of the output MOS transistor 21 and the sense MOS transistor 22 to set the output MOS transistor 21 and the sense MOS transistor 22 to an ON state.

When the output MOS transistor 21 is set to the ON state, the load current I_(OUT) is supplied to the load 3 connected with the load terminal 13 from the DC power supply 2 connected with the power supply terminal 12 through the output MOS transistor 21. FIG. 6 is a conceptual diagram showing the current path through which the load current I_(OUT) flows in the output MOS transistor 21. In FIG. 6, the path through which the load current I_(OUT) flows is shown by an arrow 45.

The load current I_(OUT) flows in a perpendicular direction to the N⁺ substrate 31 and the N-type semiconductor region 32 (a direction perpendicular to the front-side main surface 31 a of the N⁺ substrate 31), and moreover, flows into the N⁺ diffusion layer 36 through the channel which is formed in the neighborhood of the surface opposing to the gate electrode 41 of the P-type base region 34. Moreover, the load current I_(OUT) having flowed into the N⁺ diffusion layer 36 flows into the load terminal 13 through the source electrode 38 from the N⁺ diffusion layer 36, and is supplied to the load 3 connected with the load terminal 13.

When the load current I_(OUT) flows through the output MOS transistor 21, a voltage drop due to a channel resistance R_(CH) and the substrate resistance R_(SUB) is generated. Here, the channel resistance R_(CH) is a resistance of a channel which is formed in the P-type base region 34 and the substrate resistance R_(SUB) is a resistance of the N⁺ substrate 31 and the N-type semiconductor region 32 in the perpendicular direction to them. Because the resistances of the back electrode 33, the N⁺ diffusion layer 36 and the source electrode 38 can be ignored to be small as compared with the channel resistance R_(CH) and the substrate resistance R_(SUB), they are not considered in case of the following consideration.

What the inventor paid attention to is the fact that the channel resistance R_(CH) depends on the voltage between the source and the gate in the output MOS transistor 21, whereas, the substrate resistance R_(SUB) is a known fixed value which depends only on the characteristics of the N⁺ substrate 31 and the N-type semiconductor region 32. Based on these facts, the inventor reached the conclusion that the load current I_(OUT) can be measured precisely, if the voltage drop due to the substrate resistance R_(SUB) can be measured precisely when the load current I_(OUT) flows. As an example, the substrate resistance R_(SUB) can restrain a deviation (a manufacturing deviation) in a range of about ±3%. This means that a measurement error of the load current I_(OUT) due to the deviation of the substrate resistance R_(SUB) can be restrained in a range of about ±3% when the load current I_(OUT) is calculated from the voltage drop ΔV_(SUB) due to the substrate resistance R_(SUB).

Here, it could be considered that the voltage drop due to the substrate resistance R_(SUB) is equal to a voltage difference between a voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 and a voltage of the back electrode 33. However, because the boundary between the N-type semiconductor region 32 and the P-type base region 34 is inside the semiconductor chip 1, the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 cannot be measured directly. Therefore, it is required to measure the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 precisely through an indirect technique.

One utility of the structure of the semiconductor chip 1 in the present embodiment shown in FIG. 3 is in a point that the node n1 generates a voltage substantially identical with the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34. This means that the voltage drop due to the substrate resistance R_(SUB) can be measured precisely by measuring the voltage difference between the node n1 and the back electrode 33. Below, the utility of the node n1 will be considered. Note that in the present embodiment, the voltage of the node n2 corresponding to the voltage of the back electrode 33 is used instead of the voltage of the back electrode 33, to be described later in detail. However, this does not have any relation to consideration of the utility of the node n1.

FIG. 7 is an expanded view showing the structure of the neighborhood of the gate electrode 41 of the output MOS transistor 21 and the sense MOS transistor 22. As mentioned above, in the structure of the semiconductor chip 1 in the present embodiment, the P-type base region 35 and the N⁺ diffusion layer 37 are provided to have a similar structure, as well as the P-type base region 34 and the N⁺ diffusion layer 36 which configure the output MOS transistor 21. The source electrode 39 of the sense MOS transistor 22 and the node n1 are connected with the N⁺ diffusion layer 37.

When the gate electrode 41 is driven with a high voltage (for example, a voltage of about twice of the DC power supply voltage V_(CC)), an inversion layer (that is, the channel of the output MOS transistor 21) is formed in a portion of the P-type base region 34 which opposes to the gate electrode 41 and a current flows from the back electrode 33 to the source electrode 38. In FIG. 7, the resistance of the inversion layer (i.e. the channel) formed in the P-type base region 34 is expressed as the channel resistance R_(CH).

At this time, at the same time, an inversion layer (that is, a channel of the sense MOS transistor 22) is formed in a portion of the P-type base region 35 which opposes to the gate electrode 41. Moreover, an accumulation layer is formed in a portion of the N-type semiconductor region 32 which opposes to the gate electrode 41. In FIG. 7, the resistance of the inversion layer formed in the P-type base region 35 is expressed as a channel resistance R_(CH) _(_) _(n1), and the resistance due to an accumulation layer formed in the N-type semiconductor region 32 is expressed as an accumulation layer resistance R_(ACC). The channel resistance R_(CH) _(_) _(n1) and the accumulation layer resistance R_(ACC) are both variable resistances which depend on a gate voltage V_(G), and the substrate resistance R_(SUB) and R_(SUB) _(_) _(n1) are fixed resistances which do not depend on the gate voltage V_(G).

FIG. 8 is a circuit diagram schematically showing an equivalent circuit of electrical connection among the source electrodes 38 of the output MOS transistor 21, the back electrode 33 (common drain electrode) and the node n1, when the gate electrode 41 is driven with the high voltage. In the equivalent circuit, a series connection of the channel resistance R_(CH) and the substrate resistance R_(SUB) is connected between the back electrode 33 and the source electrode 38 and a series connection of the channel resistance R_(CH) _(_) _(n1) and the substrate resistance R_(SUB) _(_) _(n1) is connected between the back electrode 33 and the node n1. Moreover, the accumulation layer resistance R_(ACC) is connected between a connection node N_(A) between the channel resistance R_(CH) and the substrate resistance R_(SUB) and a connection node N_(B) between the channel resistance R_(CH) _(_) _(n1) and the substrate resistance R_(SUB) _(_) _(n1).

Here, in FIG. 8, the voltage in the connection node N_(A) is equivalent to the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34. The fact that the voltage difference between connection node N_(A) and the node n1 is small will be considered.

Here, the attention should be paid to the fact that a region of the sense MOS transistor 22 is considerably small, as compared with a region of the output MOS transistor 21. Therefore, it is assumed in the following consideration that the channel resistance R_(CH) _(_) _(n1) of the sense MOS transistor 22 is considerably greater than the channel resistance R_(CH) of the output MOS transistor 21 and the substrate resistance R_(SUB) _(_) _(n1) of the sense MOS transistor 22 is considerably greater than the substrate resistance R_(SUB) of the output MOS transistor 21. Specifically, in the following consideration, assuming that an area ratio of the output MOS transistor 21 and the sense MOS transistor 22 is 100:1, the voltage of the connection node N_(A) and the voltage of the node n1 are calculated by using the following numerical value example:

the channel resistance R_(CH) of the output MOS transistor 21: 1Ω;

the substrate resistance R_(SUB) of the output MOS transistor 21: 9Ω;

the channel resistance R_(CH) _(_) _(n1) of the sense MOS transistor 22: 100Ω;

the substrate resistance R_(SUB) _(_) _(n1) of the sense MOS transistor 22: 900Ω; and

the accumulation layer resistance R_(ACC): 10Ω.

Also, it is supposed that the voltage between the back electrode 33 (the common drain electrode) and the source electrode 38 is 0.1V (100 mV), when the voltage of the source electrode 38 of the output MOS transistor 21 is a reference voltage (0V). This is a proper value as the voltage between the source and the drain when the MOS transistor of a UMOS structure is in an ON state.

Considering a case where the current flowing through the node n1 is zero, the voltage of connection node N_(A) is calculated as 0.010 V (10 mV) from the equivalent circuit of FIG. 8. On the other hand, the voltage of the node n1 is coincident with the voltage of the connection node N_(B) and is calculated to be 0.0111 V. In other words, the voltage difference between the connection node N_(A) and the node n1 is suppressed to about 1.1 mV. It should be noted that if a comparator with the configuration of the input current of substantively zero is used, the current flowing through the node n1 can be substantively made zero, as shown in FIG. 2A.

On the other hand, in case where the current flows through the node n1, because the input current of the comparator 28 can be suppressed to several μA when the comparator with general configuration is adopted to the comparator 28 (e.g. the configuration shown in FIG. 2B-FIG. 2C is adopted), the voltage drop due to the channel resistance R_(CH) _(_) _(n1) of the sense MOS transistor 22 is less than 1 mV and the voltage difference between the connection node NA and the node n1 is still very small.

As understood from the above consideration, the voltage difference between the connection node N_(A) and the node n1, i.e. the voltage difference between the boundary between the N-type semiconductor region 32 and the P-type base region 34 and the node n1 is very small. Accordingly, the voltage drop due to the substrate resistance R_(SUB) can be precisely measured by using the voltage of the node n1.

Another utility of the structure of the semiconductor chip 1 in the present embodiment shown in FIG. 3 is in that the voltage corresponding to the voltage of the back electrode 33 (that is, the common drain electrode of the output MOS transistor 21 and the sense MOS transistor 22) can be taken out to the node n2. As understood from the above-mentioned consideration, the voltage drop due to the substrate resistance R_(SUB) of the output MOS transistor 21 is substantially coincident with the voltage difference between the node n1 and the back electrode 33. However, because circuits of the control circuit section 15, especially the set threshold voltage generating section 27 and the comparator 28 of the voltage detecting circuit 24 are formed on the front-side main surface 30 a of the semiconductor substrate 30, it is very difficult to directly connect the back electrode 33 with the voltage detecting circuit 24 in mounting.

To cope with such a problem, in the present embodiment, the N⁺ diffusion layer 42 is provided for the N-type semiconductor region 32, and a voltage taking-out electrode 43 is connected to the N⁺ diffusion layer 42. The voltage taking-out electrode 43 is connected with the above-mentioned node n2. According to such a configuration, the voltage of the voltage taking-out electrode 43 is almost coincident with the voltage of the back electrode 33 (that is, the voltage of the power supply terminal 12). Strictly speaking, when the current flows between the voltage taking-out electrode 43 and the back electrode 33, the voltage of the voltage taking-out electrode 43 is different from the voltage of the back electrode 33. However, it is possible to suppress the current flowing between the voltage taking-out electrode 43 and the back electrode 33 to a small value by sufficiently increasing the input resistance of the set threshold voltage generating section 27 viewed from the node n2, and the voltage of the node n2 can be brought close to the voltage of the back electrode 33.

In the present embodiment, the voltage of the node n1 and the voltage of the node n2 which have the nature as mentioned above are used as the inputs of the voltage detecting circuit 24. In other words, the voltage which is equivalent to the voltage drop due to the substrate resistance R_(SUB) is supplied to the voltage detecting circuit 24 as the voltage between the node n1 and the node n2. Because the voltage drop due to the substrate resistance R_(SUB) is shown by a product I_(OUT)·R_(SUB) of the load current I_(OUT) and the substrate resistance R_(SUB) it is possible to precisely detect the load current I_(OUT) by detecting the voltage between the node n1 and the node n2 by the voltage detecting circuit 24.

The voltage detecting circuit 24 outputs a detection signal S_(DET) according to the voltage between the node n1 and the node n2 (that is, according to the load current I_(OUT)), as described below. When the load current I_(OUT) is small (in a normal range), and the voltage difference ΔV21 (=Vn2−Vn1≈I_(OUT)·R_(SUB)) between the voltage Vn1 at the node n1 and the voltage Vn2 at the node n2 is lower than the set threshold voltage V_(TH), the voltage of the − input terminal becomes higher than the voltage of the + input terminal in the comparator 28 so that the detection signal S_(DET) outputted from the comparator 28 becomes a low level. On the other hand, when the load current I_(OUT) is great and the voltage difference ΔV21 between the node n1 and the node n2 is higher than the set threshold voltage V_(TH), the voltage of the − input terminal becomes lower than the voltage of the + input terminal in the comparator 28 so that the detection signal S_(DET) outputted from the comparator 28 becomes a high level. According to such an operation, by setting the set threshold voltage V_(TH) to meet the following equation (1):

V _(TH) =I _(OUT) *×R _(SUB)  (1)

according to the set value I_(OUT)* of the load current I_(OUT) to be detected, it is possible to detect that the load current I_(OUT) is greater than the specific set value I_(OUT)* or is smaller than it.

The detection signal S_(DET) outputted from the comparator 28 is supplied to the logic circuit 25, and the logic circuit 25 can realize a function of monitoring the load current I_(OUT) by referring to the detection signal S_(DET). For example, it is possible to provide for the logic circuit 25, a function of detecting over-current, i.e. a function of detecting the load current I_(OUT) exceeding the set value I_(OUT)* and turning off the output MOS transistor 21. In detail, in order to realize the function of detecting the over-current, when the detection signal S_(DET) outputted from the comparator 28 is in the high level, a logic is incorporated into the logic circuit 25 such that the control signal S_(CTRL) which controls the turning-on or -off of the output MOS transistor 21 is set to the low level regardless of the external control signal IN.

On the other hand, a function of detecting a light load (for example, part of the plurality of loads is broken) and no load (for example, an open circuit failure of the load terminal 13), i.e. a function of detecting that the load current I_(OUT) is smaller than the set value I_(OUT)* may be provided for the logic circuit 25. In this case, in the embodiment, the logic circuit 25 may be incorporated with the logic of determining that the load current I_(OUT) fell below the set value I_(OUT)*, in response to the detection signal S_(DET) in the low level outputted from the comparator 28 and outputting an error signal to a specific external terminal (e.g. a diagnosis terminal).

When incorporating two of the function of detecting the over-current, the function of detecting the light load, and the function of detecting of no load into the semiconductor chip 1, it is sufficient to provide two sets of the set threshold voltage generating section 27 and two the comparators 28. A configuration example of the semiconductor chip 1 in this case is shown in FIG. 9. In the semiconductor chip 1 of FIG. 9, the voltage detecting circuit 24 has two comparators 28 a and 28 b, and two set threshold voltage generating sections 27 a and 27 b. The set threshold voltage generating sections 27 a and 27 b have respective voltage sources which generate desired set threshold voltages V_(TH1) and V_(TH2). The terminals of the set threshold voltage generating sections 27 a and 27 b on the higher voltage side are connected to the node n2 in common, and the terminals thereof on the lower voltage side are respectively connected with the + input terminals (non-inversion inputs) of the comparators 28 a and 28 b. That is, the + input terminals of the comparators 28 a and 28 b are respectively set to the voltages lower by the voltages V_(TH1) and V_(TH2) than the voltage at the node n2.

The comparator 28 a compares the voltage of the + input terminal and the voltage of the − input terminal (inversion input) and generates a detection signal S_(DET1) corresponding to the comparison result. In the same way, the comparator 28 b compares the voltage of the + input terminal and the voltage of the − input terminal (inversion input) and generates a detection signal S_(DET2) corresponding to the comparison result. The detection signals S_(DET1) and S_(DET2) generated by the comparators 28 a and 28 b are supplied to the logic circuit 25 and are used for realization of two of the functions of the detection of the over-current, the detection of the light load and the detection of no load.

In the same way, when three functions of the detection of the over-current, the detection of the light load and the detection of no the load are incorporated into the semiconductor chip 1, it is sufficient to provide three sets of the set threshold voltage generating section 27 and the comparator 28 (not shown).

As described above, the semiconductor device of the present embodiment can detect the load current I_(OUT) in a high precision. There are two factors of the improvement of the detection precision of the load current I_(OUT).

A first factor of the improvement of the detection precision of the load current I_(OUT) is in that the load current I_(OUT) is detected based on the voltage drop due to the substrate resistance R_(SUB). A deviation of the substrate resistance R_(SUB) can be restrained to about ±3% in absolute precision, as an example. Therefore, the detection precision of the load current LOUT can be improved to a high precision by detecting the load current I_(OUT) from the voltage drop due to the substrate resistance R_(SUB). Indicating a more specific calculation example, when the set threshold voltage V_(TH) is 100 mV and the deviation of ±3 mV exists in the input offset voltage of the comparator 28, the detection error of ±3% in the substrate resistance R_(SUB) and the detection error of the deviation of ±3% in the input offset voltage are generated. That is, the detection error of about ±6% in the load current I_(OUT) can be obtained in this calculation example in the worst case.

In the Patent Literature 2, a sense current which is proportional to a load current is generated by a sense MOS transistor, and a detection voltage is generated by the sense current flowing through a sense resistance which is formed from a metal wiring line. Because the absolute value of a resistance value is very small in the metal wiring although a deviation of the resistance value is suppressed to a small value, the absolute value of the detection voltage is very small. In other words, the set threshold voltage V_(TH) of the comparator needs to be made very small and the influence of a deviation of the input offset voltage of the comparator is relatively strong.

On the other hand, in the Patent Literature 3, a sense current which is proportional to a load current is generated by a sense MOS transistor, and is received by a current mirror circuit of bipolar transistors so as to generate a mirror current of the sense current. Then, the mirror current of a current set by a constant current source is generated as a reference current and is compared with the mirror current of the sense current so as to detect a current of a power MOS transistor. Moreover, in the Patent Literature 3, a voltage between a base and an emitter in a bipolar transistor connected with the sense MOS transistor in series reduces the precision of the sense current. For this reason, a constant current source is inserted to cancel the reduction so that the detection precision is improved. However, in the Patent Literature 3, it could be thought that the precision of the sense current is improved. However, the precision of the reference current, i.e. the precision of the constant current source influences the detection precision directly. In a general semiconductor manufacture line, a deviation (manufacture deviation) of the constant current source formed on the semiconductor substrate is expected as about ±30%. Thus, it is considerably difficult to suppress the manufacture deviation to about ±3% which is almost same as the deviation of the substrate resistance R_(SUB).

A second factor is in that the voltage which is substantially coincident with a voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 is generated at the node n1. As considered above, in order to precisely measure the voltage drop due to the substrate resistance R_(SUB), it is necessary to precisely measure the voltage difference between the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 and the voltage at the back electrode 33. Here, in the semiconductor device of the present embodiment, the boundary between the N-type semiconductor region 32 and the P-type base region 34 is electrically connected with the node n1 in a low resistance through an accumulation layer formed in the N-type semiconductor region 32 and an inversion layer formed in the P-type base region 35. Therefore, the voltage which is substantially coincident with the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 is generated at the node n1. The voltage at the node n1 is supplied to the voltage detecting circuit 24 as an input. Therefore, the semiconductor device of the present embodiment can precisely measure the voltage drop due to the substrate resistance R_(SUB).

On the other hand, referring to FIG. 1 and FIG. 2 in the Patent Literature 1, a current detection electrode 9 for the detection of a voltage drop of the silicon substrate is formed in the substrate surface apart from a position where a collector current flows most strongly (a position of the boundary between an base diffusion layer 3 and an epitaxial silicon layer 2 under an emitter electrode 7). In other words, the Patent Literature 1 can acquire only a detection precision which contains the voltage drop due to the epitaxial silicon layer 2 from the position of the boundary between the epitaxial silicon layer 2 and the base diffusion layer 3 under the emitter electrode 7 to the current detection electrode 9.

It should be noted that in the semiconductor device of the present embodiment, the structure of the output MOS transistor 21 and the sense MOS transistor 22 is not limited to the structure shown in FIG. 3, and it is possible to change variously. For example, in FIG. 3, the UMOS structure that the film thickness of the gate insulating film 40 is uniform is shown but the structure may be adopted in which the film thickness of the gate insulating film 40 is thick in the bottom of the trench which reaches the N-type semiconductor region 32 as shown in FIG. 10. In this case, there is a possibility that the resistance of the accumulation layer formed in the surface opposing to the gate electrode 41 in the N-type semiconductor region 32 increases, so that the voltage difference between the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 and the voltage at the node n1 increases. However, in such a structure, because the output MOS transistor 21 and the sense MOS transistor 22 are in just near positions, it is possible to enjoy the advantage of the semiconductor device according to the above-mentioned embodiment for an extent.

Also, a double gate structure may be adopted in which the trenches are formed to reach the N⁺ substrate 31 as shown in FIG. 11 and two gate electrodes 41 a and 41 b are embedded in each trench. In FIG. 11, the gate electrode on the underside is shown by 41 a and the gate electrode on the topside is shown by 41 b. The gate electrodes 41 a and 41 b are electrically connected to each other. That is, the gate electrodes 41 a and 41 b are driven with an identical voltage. In this case, the accumulation layers are formed in the surface section opposing to the gate electrode 41 a in the N-type semiconductor region 32 and the surface section opposing to the gate electrode 41 a of the N⁺ substrate 31 when the gate electrodes 41 a and 41 b are driven. Therefore, the voltage which is approximately coincident with the voltage at the boundary between the N-type semiconductor region 32 and the P-type base region 34 can be generated in the node n1.

Also, as shown in FIG. 12, a DMOS (double-diffused MOS) structure may be used for the output MOS transistor 21 and the sense MOS transistor 22. In detail, the semiconductor substrate 30 has the P-type base regions (the body region) 46 and 48 formed on the N-type semiconductor region 32, and the N⁺ diffusion layers 47 and 49 are formed in the P-type base regions 46 and 48. The P-type base regions 46 and 48 are the semiconductor regions where a P-type impurity is doped, and also, the N⁺ diffusion layers 47 and 49 are the semiconductor regions where an N-type impurity is heavily doped. The P-type base region 46 is a region where the channel of the output MOS transistor 21 is formed and the P-type base region 48 is a region where the channel of the sense MOS transistor 22 is formed. In the present embodiment, a part of the N-type semiconductor region 32 exists between the P-type base region 46 and the P-type base region 48. The N-type semiconductor region 32 reaches the front-side main surface 30 a of the semiconductor substrate 30 by passing between the P-type base region 46 and the P-type base region 48. Also, the N⁺ diffusion layer 47 functions as a source of the output MOS transistor 21 and the N⁺ diffusion layer 49 functions as a source of the sense MOS transistor 22.

Moreover, the source electrode 38 is formed to be joined with the N⁺ diffusion layer 47, and the source electrode 39 is formed to be joined with the N⁺ diffusion layer 49. That is, the source electrode 38 is electrically connected with the source of the output MOS transistor 21 and the source electrode 39 is electrically connected with the source of the sense MOS transistor 22. The source electrode 38 is connected with the load terminal 13 and the source electrode 39 is connected with the node n1.

Moreover, the gate insulating film 51 is formed to partially cover a surface of the P-type base regions 46 and 48 and the N-type semiconductor region 32, and the gate electrode 52 is formed on the gate insulating film 51. Note that the gate electrode 52 is provided to oppose to a part of the surface of the P-type base regions 46 and 48 and to oppose to a part of the surface of the N-type semiconductor region 32.

In case where the DMOS structure shown in FIG. 12 is adopted, when a positive voltage which exceeds the threshold voltages of the output MOS transistor 21 and the sense MOS transistor 22 is applied to the gate electrode 52, the voltage which is approximately identical with the voltage at the boundary between the P-type base region 46 and the N-type semiconductor region 32 can be taken out from the node n1. FIG. 13 is a diagram showing the route through which the load current I_(OUT) flows when the positive voltage which exceeds the threshold voltage is applied to the gate electrode 52 in the semiconductor device having the structure of FIG. 12 (that is, when the output MOS transistor 21 is turned on). The route through which the load current I_(OUT) flows is shown by an arrow 45 in FIG. 13.

When the gate electrode 52 is driven with a high voltage (for example, about twice of the DC power supply voltage V_(CC)), an inversion layer is formed in the surface of the P-type base region 46 opposing to the gate electrode 52. The inversion layer is used as the channel of the output MOS transistor 21. The load current I_(OUT) flows in the perpendicular direction from the N⁺ substrate 31 and flows into the N⁺ diffusion layer 47 through the channel formed in the P-type base region 46. Moreover, the load current I_(OUT) which flows into the N⁺ diffusion layer 47 is supplied to the load 3 connected with the load terminal 13, flowing into the load terminal 13 through the source electrode 38 from the N⁺ diffusion layer 47.

At this time, the inversion layer (that is, the channel of the sense MOS transistor 22) is formed in the surface of the P-type base region 48 opposing to the gate electrode 52, and an accumulation layer is formed in the surface of the N-type semiconductor region 32 opposing to the gate electrode 52. Therefore, the boundary between the P-type base region 46 and the N-type semiconductor region 32 is electrically connected with the node n1 in a lower resistance and the voltage which is approximately identical with the voltage at the boundary between the P-type base region 46 and the N-type semiconductor region 32 can be taken out from the node n1. It is useful to precisely measure the voltage drop due to the substrate resistance R_(SUB), i.e. to precisely measure the load current I_(OUT) that the voltage which is approximately identical with the voltage at the boundary between the P-type base region 46 and the N-type semiconductor region 32 is taken out from the node n1.

Also, as shown in FIG. 14, IGBT (insulated gate bipolar transistor) may be used as a power transistor, instead of the output MOS transistor 21 and the sense MOS transistor 22. In FIG. 14, the IGBT which is used instead of the output MOS transistor 21 is shown as an output IGBT 21A and an IGBT which is used instead of the sense MOS transistor 22 is shown as a sense IGBT 22A. In the configuration of FIG. 14, a collector region 31 c into which the P-type impurity is heavily doped and a drain region 31 d into which the N-type impurity is heavily doped are used instead of the N⁺ substrate 31. Here, the back electrode 33 is joined with the collector region 31 c and the drain region 31 d is joined with the collector region 31 c. Moreover, the N-type semiconductor region 32 is joined with the drain region 31 d. As well-known, the IGBT is a device in which both of electrons and holes can be used as carriers by adopting the structure that a collector region is additionally provided for the MOS transistor. Therefore, the structure of the semiconductor device in which the output IGBT 21A and the sense IGBT 22A are provided as the power transistors as shown in FIG. 14 does not have an essential difference from the structure that the output MOS transistor 21 and the sense MOS transistor 22 are provided as shown in FIG. 3.

That is, when the gate electrode 52 is driven in the high voltage (for example, about twice of the DC power supply voltage V_(CC)) as shown in FIG. 15, the inversion layer is formed in the surface of the P-type base region 46 opposing to the gate electrode 52. This inversion layer is used as the channel of the output MOS transistor 21. The load current I_(OUT) flows in the perpendicular direction from the collector region 31 c and flows into the N⁺ diffusion layer 47 through the channel formed in the P-type base region 46. Moreover, the load current I_(OUT) which flows into the N⁺ diffusion layer 47 is supplied to the load 3 connected with the load terminal 13, flowing into the load terminal 13 through the source electrode 38 from the N⁺ diffusion layer 47.

At this time, the inversion layer (that is, the channel of the sense MOS transistor 22) is formed in the surface of the P-type base region 48 opposing to the gate electrode 52, and the accumulation layer is formed in the surface of the N-type semiconductor region 32 opposing to the gate electrode 52. Therefore, the boundary between the P-type base region 46 and the N-type semiconductor region 32 is electrically connected with the node n1 in a low resistance and the voltage which is approximately identical with the voltage at the boundary between the P-type base region 46 and the N-type semiconductor region 32 can be taken out from the node n1. As considered above, it is useful to precisely measure the voltage drop due to the substrate resistance R_(SUB), i.e. to precisely measure the load current I_(OUT) that the voltage which is approximately identical with the voltage at the boundary between the P-type base region 46 and the N-type semiconductor region 32 is taken out from the node n1.

It should be noted that in the present embodiment, the substrate resistance in the collector region 31 c is not used. The drain region 31 d is common, the drain region 31 d and the N-type semiconductor region 32 are used as the substrate resistance R_(SUB) and the voltage which is approximately identical with the drain region 31 d is taken out from the node n2.

FIG. 16 is a sectional view showing a further modification example of the semiconductor device of the present embodiment. Moreover, in the structure of FIG. 16, an N⁺ region 53 is formed to reach the N⁺ substrate 31 through the N-type semiconductor region 32 from the front-side main surface 30 a of the semiconductor substrate 30, and a common drain electrode 54 is connected with the N⁺ region 53. The N⁺ region 53 is a semiconductor region where the N-type impurity is heavily doped. In the structure of FIG. 16, the power supply terminal 12 is connected to the common drain electrode 54, and also, the node n2 is connected with the common drain electrode 54. That is, when the structure of FIG. 16 is adopted, the voltage at the node n2 is substantially coincident with the voltage of the common drain electrode 54.

In a configuration as shown in FIG. 16, because the common drain electrode 54 is formed on the front-side main surface 30 a of the semiconductor substrate 30, the connection between the circuits of the control circuit section 15 (which are formed on the front-side main surface 30 a of the semiconductor substrate 30) and the common drain electrode 54 is easy, and is favorable in case of implementing of the semiconductor device of the present embodiment. In other words, because all of the external terminals can be formed on the front-side main surface of the semiconductor chip, the so-called flip-chip implementing becomes possible.

It should be noted that in the configuration of FIG. 16, the back electrode 33 is used to reduce a resistance of the N⁺ substrate in the surface in the direction in the surface, not connection terminals with the external unit. The semiconductor device of the structure of FIG. 16 carries out the same operation as the semiconductor device of the structure of FIG. 3, excluding that the load current I_(OUT) flows into the N⁺ substrate 31 through the common drain electrode 54 and the N⁺ region 53 from the power supply terminal 12. Also, when the resistance in the direction to the surface of the N⁺ substrate 31 is sufficiently small, the back electrode 33 may be removed, as shown in FIG. 17.

Second Embodiment

FIG. 18 is a block diagram showing a configuration of the semiconductor device according to a second embodiment. In the present embodiment, the semiconductor chip 1A is not a high side driver IC as shown in FIG. 1, and is configured as a so-called low side driver IC which is provided between the load 3 and the ground terminal 4. Hereinafter, the configuration of the semiconductor chip 1A will be described in detail.

The semiconductor chip 1A has a load terminal 13A connected with the load 3 and a ground terminal 12A connected with a ground terminal 4 (i.e. ground) and is configured to switch the electrical connection between the load 3 and the ground terminal 4. In detail, an output device section 14 and a control circuit section 15A are integrated in a monolithic manner on the semiconductor chip 1A. The configuration of the output device section 14 of the semiconductor chip 1A is identical with the output device section 14 of the semiconductor chip 1 of the first embodiment. On the other hand, the control circuit section 15A is configured to make the semiconductor chip 1A operate as the low side driver IC.

The control circuit section 15A is configured from a control circuit block 23A and a voltage detecting circuit 24. The configuration of the voltage detecting circuit 24 is identical with that of the voltage detecting circuit 24 of the semiconductor chip 1 in the first embodiment, and has the set threshold voltage generating section 27 and the comparator 28. As considered in the first embodiment in detail, the voltage detecting circuit 24 generates the detection signal S_(DET) according to a voltage difference ΔV21 (=Vn2−Vn1) between the voltage Vn1 of the node n1 and the voltage Vn2 of the node n2.

The control circuit block 23A is configured from a gate resistance 71, an input circuit 72 and an NMOS transistor 73. The gate resistance 71 is connected between a gate connection node NG connected with the gate of the output MOS transistor 21 and the sense MOS transistor 22 (i.e. the gate electrode 41) and the control input terminal 11. The input circuit 72 turns on or off the NMOS transistor 73 in response to the external control signal IN which is supplied to the control input terminal 11 and the detection signal S_(DET) outputted from the voltage detecting circuit 24. Note that the voltage of the external control signal IN which is supplied to the control input terminal 11 is used as the DC power supply voltage of an input circuit 72. The NMOS transistor 73 is used as a short-circuiting switch which connects the gate connection node NG and the ground terminal 12A under the control of the input circuit 72. A drain of the NMOS transistor 73 is connected with the gate of the output MOS transistor 21 and the sense MOS transistor 22, and a source thereof is connected with the ground terminal 12A.

FIG. 19 is a sectional view showing a structure of the output MOS transistor 21 and the sense MOS transistor 22 in the semiconductor device of the second embodiment. As shown in FIG. 19, the structure of the output MOS transistor 21 and the sense MOS transistor 22 in the second embodiment is the same as that of the first embodiment shown in FIG. 3, excluding that the back electrode 33 is connected with a load terminal 13A instead of the load terminal 13 and the source electrode 38 is connected with the ground terminal 12A instead of the power supply terminal 12.

Next, the operation of the semiconductor device in the second embodiment will be described. Referring to FIG. 18 again, it is supposed that the external control signal IN is set to the low level in an initial state. In this case, the output MOS transistor 21 and the sense MOS transistor 22 are both turned off so that the load current I_(OUT) does not flow.

When the external control signal IN is set to the high level (a voltage level which is higher than the threshold voltages of the output MOS transistor 21 and the sense MOS transistor 22), the output MOS transistor 21 is turned on. At this time, the input circuit 72 sets the gate of the NMOS transistor 73 to the low level, to turn off the NMOS transistor 73. When the output MOS transistor 21 is turned on, a current path from the load 3 to the ground terminal 4 is formed so that the load current I_(OUT) flows from the load 3 to the ground terminal 12A.

The operation of detecting the load current I_(OUT) when the output MOS transistor 21 is set to the ON state, is the same as that of the first embodiment. When the load current I_(OUT) flows through the output MOS transistor 21, like the first embodiment, the voltage drop due to the channel resistance R_(CH) and the substrate resistance R_(SUB) occurs. The voltage drop due to the substrate resistance R_(SUB) is detected as a voltage difference between the node n1 and the voltage of the node n2 by the voltage detecting circuit 24.

Here, in the second embodiment, the input circuit 72 operates according to the detection signal S_(DET) outputted from the voltage detecting circuit 24. When a function of detecting over-current is incorporated in the input circuit 72, the input circuit 72 determines that the load current I_(OUT) exceeds a set value I_(OUT)* when the detection signal S_(DET) is in the high level, and turns on the NMOS transistor 73 regardless of the external control signal IN. Thus, the source and the gate in the output MOS transistor 21 are connected so that the output MOS transistor 21 is compulsorily set to the OFF state regardless of the external control signal IN. Also, when a function of detecting light load (or no load) implemented in the input circuit 72, the input circuit 72 determines that the load current I_(OUT) falls below the set value I_(OUT)* when the detection signal S_(DET) is in the low level, and outputs an error signal to a specific external terminal (e.g. a diagnosis terminal which is not shown).

Third Embodiment

FIG. 20 is a sectional view showing a configuration of a semiconductor device 1B in a third embodiment, and FIG. 21 is a plan view showing a configuration of the semiconductor device 1B. As shown in FIG. 20 and FIG. 21, the semiconductor device 1B of the present embodiment includes two chips: an output device chip 5 and a control circuit chip 6. The output device chip 5 is a semiconductor chip which has the same configuration and functions as those of the output device section 14 in the first and second embodiments and the control circuit chip 6 is a semiconductor chip which has the same configuration and functions as those of the control circuit section (15 or 15 A) in the first or second embodiment.

As shown in FIG. 20, the output MOS transistor 21 and the sense MOS transistor 22 which have the same structure as the output device section 14 in the first and second embodiments are integrated on the output device chip 5. In detail, the output device chip 5 includes the semiconductor substrate 30 having the N⁺ substrate 31 and the N-type semiconductor region 32 formed on the front-side main surface 31 a of the N⁺ substrate 31. The back electrode 33 is formed on the back-side main surface of the semiconductor substrate 30, i.e. the back-side main surface 31 b of the N+ substrate 31, and this back electrode 33 is connected with the power supply terminal 12 to which the DC power supply voltage V_(CC) is supplied. The P-type base regions 34 and 35 (body regions) are formed on the N-type semiconductor region 32, and the N⁺ diffusion layers 36 and 37 are formed on the P-type base regions 34 and 35. The N⁺ diffusion layers 36 and 37 are provided to be in contact with the front-side main surface 30 a of the semiconductor substrate 30. Moreover, the source electrode 38 is formed to be joined to the N⁺ diffusion layer 36, and the source electrode 39 is formed to be joined to the N⁺ diffusion layer 37. The source electrode 38 is connected with the load terminal 13 and the source electrode 39 is connected with the node n1. Note that the node n1 is connected with one of the input terminals of the comparator 28 which carries out the voltage detection (− input terminal), as mentioning above. Moreover, a trench is formed in the semiconductor substrate 30 to pass through the P-type base regions 34 and 35 (where the N⁺ diffusion layers 36 and 37 are formed) to the N-type semiconductor region 32, and the gate insulating film 40 is formed to cover the side surface and base surface of the trench. Moreover, the gate electrode 41 is formed on the gate insulating film 40 to fill the trench.

Also, circuits which are the same as those of the control circuit section (15 or 15 A) in the first or second embodiment are integrated on the control circuit chip 6 and a structure for taking out the voltage of the power supply terminal 12 (the voltage of the common drain electrode) is provided for the node n2. In detail, the control circuit chip 6 has a semiconductor substrate 80 and the semiconductor substrate 80 has an N⁺ substrate 81 and an N-type semiconductor region 82 formed on the front-side main surface of the N⁺ substrate 81. The N-type impurity is heavily doped into the N⁺ substrate 81. The back electrode 83 is joined with the back-side main surface of the N⁺ substrate 81. Also, the N-type impurity is doped into the N-type semiconductor region 82. Circuits which are the same as those of the control circuit section (15 or 15A) in the first and second embodiments are integrated on the surface section of the N-type semiconductor region 82 and the N⁺ diffusion layer 42 is formed. The voltage taking-out electrode 43 is connected with the N⁺ diffusion layer 42 and the voltage taking-out electrode 43 is connected with the node n2.

The back electrode 33 of the output device chip 5 and the back electrode 83 of the control circuit chip 6 are joined to a die pad 7 formed of a conductive material, and the power supply terminal 12 is connected to the die pad 7. The back electrode 33 of the output device chip 5 and the back electrode 83 of the control circuit chip 6 are electrically connected by the die pad 7 and have substantially the same voltage. Therefore, the voltage which is the same voltage (the voltage of the common drain electrode) as that of the back electrode 33 of the output device chip 5 or a corresponding voltage is taken out to the node n2.

FIG. 21 is a diagram showing the implementing of the output device chip 5 and the control circuit chip 6 in the semiconductor device 1B of a third embodiment. Pads 84, 85 and 86 are integrated on the output device chip 5, in addition to the output MOS transistor 21 (only the source electrode 38 is shown in FIG. 21), the sense MOS transistor 22 (only the source electrode 39 is shown in FIG. 21), an output gate wiring line 55, a ring wiring line 56 and an output source wiring line 57. The output gate wiring line 55 is connected with the pad 84, the output source wiring line 57 is connected with the pad 85 and the node n1 is connected with the pad 86.

On the other hand, pads 87, 88 and 89 are integrated on the control circuit chip 6, in addition to the control circuit block 23 (or 23 A), the set threshold voltage generating section 27, the comparator 28 and the voltage taking-out electrode 43.

An electrical connection between the output device chip 5 and the control circuit chip 6 is attained by the die pad 7 and bonding wires 91, 92 and 93. As mentioned above, the back electrode 33 of the output device chip 5 and the back electrode 83 of the control circuit chip 6 are electrically connected by the die pad 7. Also, the pads 84, 85 and 86 of the output device chip 5 are connected with the pads 87, 88 and 89 of the control circuit chip 6 by bonding wires 91, 92 and 93, respectively. The control circuit block 23 (or 23A) is connected with the output gate wiring line 55 through the pad 87, the bonding wire 91 and the pad 84, and is connected with the output source wiring line 57 through the pad 88, the bonding wire 92 and the pad 85. Moreover, the node n1 (the source electrode 39 of the sense MOS transistor 22) is connected with the − input terminal of the comparator 28 through the pad 86, the bonding wire 93 and the pad 89.

The configuration of the semiconductor device 1B in the above-mentioned embodiment is advantageous when the output device chip 5 and the control circuit chip 6 are formed in separate semiconductor processes. The output device chip 5 must be manufactured in the semiconductor process which fits with the semiconductor process of a power transistor, whereas it is possible to manufacture the control circuit chip 6 in the general semiconductor process. It is sometimes advantageous depending on the structure of the circuits to be integrated that the output device chip 5 and the control circuit chip 6 are formed in the separate semiconductor processes.

In the structure of FIG. 20 and FIG. 21, an electrical connection between the die pad 7 and the node n2 is attained by the structure integrated on the control circuit chip 6 (specifically, the back electrode 83, the N⁺ substrate 81, the N-type semiconductor region 82, the N⁺ diffusion layer 42 and the voltage taking-out electrode 43). However, the die pad 7 and the node n2 may be electrically connected with a different structure.

FIG. 22 is a sectional view showing a modification example of the structure of the semiconductor device in the present embodiment, and FIG. 23 is a plan view. In the semiconductor device 1C shown in FIG. 22 and FIG. 23, the die pad 7 and the node n2 are electrically connected by using a pad 90 and a bonding wire 94. The use of the bonding wire 94 is effective when the semiconductor substrate having the structure is used in which it is difficult to take out the voltage of the back-side main surface to the front-side main surface.

In detail, the semiconductor device 1C shown in FIG. 22 and FIG. 23 includes a control circuit chip 6A instead of the control circuit chip 6. The control circuit chip 6A has a semiconductor substrate 80A, and the semiconductor substrate 80A has a P-type substrate 81A and an N-type semiconductor region 82. A P-type impurity has been doped into the P-type substrate 81A. The N-type semiconductor region 82 is formed on the front-side main surface of the P-type substrate 81A, and the back electrode 83 is joined to the back-side main surface of the N⁺ substrate 81. The same circuits as the circuits contained in the control circuit section (15 or 15 A) of the first or second embodiment are integrated in the surface section of the N-type semiconductor region 82. The wiring line structure 95 having a metal wiring line layer and an interlayer insulating layer on the N-type semiconductor region 82 is formed, and the pad 90 is provided for the wiring line structure 95. The wiring line structure 95 contains a wiring line used as the node n2, and the pad 90 is connected with the wiring line, i.e. the node n2 as shown in FIG. 23. The die pad 7 is connected with the pad 90 by a bonding wire 94. By such a configuration, the back electrode 33 of the output device chip 5 (i.e. a common drain electrode) is electrically connected with the node n2 by the die pad 7, the bonding wire 94 and the pad 90. That is, the pad 90 is used as the voltage taking-out electrode which takes out the voltage of the back electrode 33 (the common drain electrode) through the die pad 7 and the bonding wire 94. The same voltage as the voltage of the back electrode 33 of the output device chip 5 (the voltage of the common drain electrode) or a corresponding voltage is taken out from the node n2.

Fourth Embodiment

FIG. 24 is a diagram schematically showing the configuration of the semiconductor device in a fourth embodiment. As shown in FIG. 1, the semiconductor device of the fourth embodiment is a modification of the semiconductor device in the first embodiment and is similar in the point that the load current I_(OUT) is detected in a high precision by taking out the voltage drop due to the substrate resistance R_(SUB) in a high precision by using the sense MOS transistor 22. However, the semiconductor device in the fourth embodiment differs from the semiconductor device of the first embodiment in the point that the taken-out voltage to the node n1 is used for the realization of a current sense output function in a high precision, i.e. the generation of the sense current I_(S) which is proportional to the load current I_(OUT). Hereinafter, the semiconductor device of the fourth embodiment will be described in detail.

The semiconductor device of the fourth embodiment has a semiconductor chip 1D in which the output device section 14D and the control circuit section 15D are integrated. The output device section 14D has substantially the same configuration as that of the output device section 14 of the first embodiment, but differs from the output device section 14 in the configuration for taking an electrical connection with a node n3. Here, the node n3 is a node connected with the power supply terminal 12 (or the common drain electrode) through the substrate resistance R_(SUB)′ as an equivalent circuit. The structure for the electrical connection with the node n3 will be described later. That is, the node n3 also has a voltage which depends on the voltage of the power supply terminal 12 (or the common drain electrode) (or, the voltage corresponding to the voltage of the power supply terminal 12).

The control circuit section 15D includes a control circuit block 23 which has the same configuration as the first embodiment, and the sense amplifier circuit 74. In detail, the control circuit block 23 has the logic circuit 25 and the charge pump 26. The logic circuit 25 generates the control signal S_(CTRL) in response to the external control signal IN, to control the charge pump 26. The charge pump 26 operates as a drive circuit to drive the gates of the output MOS transistor 21 and the sense MOS transistor 22 in response to the control signal. S_(CTRL) supplied from the logic circuit 25 and generates the gate voltage V_(G) to be supplied to the gates of the output MOS transistor 21 and the sense MOS transistor 22.

The sense amplifier circuit 74 has a sense amplifier 75 and a PMOS transistor 76 and operates as a sense current control circuit to control a sense current I_(S) according to a voltage difference between the node n1 and the node n3 in the voltage. The + input terminal (non-inversion input) of the sense amplifier 75 is connected with the node n1 and the − input terminal (inversion input) thereof is connected with the node n3. The output terminal of the sense amplifier 75 is connected with the gate of the PMOS transistor 76. The sense amplifier 75 operates as the voltage detecting circuit to output the voltage corresponding to the voltage difference between the voltage of the + input terminal (that is, the voltage of the node n1) and the voltage of the − input terminal (that is, the voltage of the node n3). The PMOS transistor 76 has a source connected with the node n3, a drain connected with the sense current terminal 16. The sense current terminal 16 is a terminal from which the sense current I_(S) flows, and when an external resistance R_(EX) is connected′ between the sense current terminal 16 and the ground terminal 8, the sense current I_(S) flows through the external resistance R_(EX). As mentioned later, the sense amplifier circuit 74 has a function of carrying out a negative feedback operation by using the voltage drop due to the substrate resistance R_(SUB)′ such that the voltage of the node n1 and the voltage of the node n3 are coincident with each other, and the sense current I_(S) which is proportional to the load current I_(OUT) is drawn out from the node n3 through this negative feedback operation.

FIG. 25 is a sectional view showing the structure of the semiconductor chip 1D in the fourth embodiment, especially the structure of the output device section 14D. The structure of the semiconductor chip 1D in the fourth embodiment is similar to the structure of the semiconductor chip 1 in the first embodiment, but different from the first embodiment in that the structure for electrical connection with the node n3 is provided whereas the structure for electrical connection with the node n2 is not provided.

In detail, a trench is formed in the semiconductor substrate 30 to pass through the P-type base region 34 from the front-side main surface to the N-type semiconductor region 32. An insulating film 61 is formed on the side of the trench and a remaining part of the trench is filled with the voltage taking-out electrode 58. The voltage taking-out electrode 58 has a metal section 58 a and a polysilicon portion 58 b. The polysilicon portion 58 b is joined with the N-type semiconductor region 32 in the bottom of the trench and the metal portion 58 a is joined with the polysilicon portion 58 b. That is, the voltage taking-out electrode 58 is joined with the N-type semiconductor region 32 in the bottom of the trench. It is ideal that a position, in the depth direction, of the plane at which the voltage taking-out electrode 58 is connected with the N-type semiconductor region 32 is identical with the junction plane between the P-type base region 34 and the N-type semiconductor region 32. In such a structure, it is possible to directly take out the voltage of the surface plane of the N-type semiconductor region 32 in the bottom of the trench to the node n3. Note that the voltage taking-out electrode 58 is provided in the neighborhood of the output MOS transistor 21. As mentioned later, it is useful in improvement of the precision of the sense current I_(S) that the voltage taking-out electrode 58 is provided in the neighborhood of the output MOS transistor 21.

In the embodiment, the voltage taking-out electrode 58 is formed in the following process. The trench to be filled or embedded with the voltage taking-out electrode 58 is formed simultaneously with the trench which is filled or embedded with the gate insulating film 40 and the gate electrode 41 (in the identical process). After the trench is formed, the gate insulating film 40 is formed over the whole of the surface of trench. Moreover, the gate insulating film 40 is removed only from the bottom of the trench to be filled with the voltage taking-out electrode 58. Thus, the trench becomes slightly deeper than the junction plane of the P-type base region 34 and the N-type semiconductor region 32, but an insulating film 61 is formed on the side of the trench to the position which is deeper than the junction plane so that the insulation between the voltage taking-out electrode 58 and the P-type base region 34 is secured. Thereafter, a polysilicon layer with impurity heavily doped is embedded in the inside of the trench to form the gate electrode 41. The polysilicon layer with the impurity heavily doped is embedded inside the trench in which the voltage taking-out electrode 58 should be embedded. However, almost part of the polysilicon layer is removed by etching, remaining the polysilicon layer of the thickness necessary to secure ohmic contact with the N-type semiconductor region 32. The remaining part is used as the polysilicon part 58 b. Next, the remaining part of the trench is embedded with a metal part 58 a. It is desirable that the voltage taking-out electrode 58 is a low resistance and it may be desirable to form the whole of electrode with metal in this viewpoint. However, because there is a fear that a contact resistance between the metal and the N-type semiconductor region 32 becomes high when the whole of voltage taking-out electrode 58 is formed of metal, the structure of the voltage taking-out electrode 58 of the metal part 58 a and the polysilicon part 58 b is used in the present embodiment. Note that the forming process of the voltage taking-out electrode 58 does not use the forming process of the gate electrode 41 and may be executed as another process.

FIG. 26 is a diagram showing a path through which the current flows, in the output device section 14D of the semiconductor chip 1D in the fourth embodiment. The path through which the load current I_(OUT) flows in FIG. 26 is shown by an arrow 45 and the path through which the sense current I_(S) flows is shown by an arrow 59.

The load current I_(OUT) flows almost through the N⁺ substrate 31 and the N-type semiconductor region 32 in a vertical direction (a direction which is orthogonal to the front-side main surface 31 a of the N⁺ substrate 31), and then flows into the N⁺ diffusion layer 36 through a channel which is formed in the neighborhood of the surface of the P-type base region 34 opposing to the gate electrode 41. The load current I_(OUT) which has flowed into the N⁺ diffusion layer 36 flows into the load terminal 13 through the source electrode 38 from the N⁺ diffusion layer 36, and is supplied to the load 3 connected with the load terminal 13.

On the other hand, the sense current I_(S) almost flows into the voltage taking-out electrode 58 through the N⁺ substrate 31 and the N-type semiconductor region 32 in a vertical direction and then flows into the node n3 from the voltage taking-out electrode 58. Therefore, the node n3 is electrically connected with the back electrode 33 through the substrate resistance R_(SUB)′. Here, when the trench filled with the voltage taking-out electrode 58 is formed simultaneously with the trench filled with the gate insulating film 40 and the gate electrode 41 (in the identical process), the depths of both trenches are substantially identical. In this case, the resistance per unit area in the vertical direction to the back surface of the semiconductor substrate 30 (back-side main surface 31 b of the substrate 31) is substantially the same between the substrate resistance R_(SUB)′ and the substrate resistance R_(SUB).

Next, the operation of the semiconductor device in the fourth embodiment will be described.

Referring to FIG. 24, it is supposed that the external control signal IN is set to the low level in the initial state. In this case, the control signal S_(CTRL) is set to the low level by the logic circuit 25 and the charge pump 26 does not drive the gate electrode 41 of the output MOS transistor 21 and the sense MOS transistor 22. Therefore, the output MOS transistor 21 and the sense MOS transistor 22 are turned off and the load current I_(OUT) does not flow.

When the external control signal IN is set to the high level, the output MOS transistor 21 and the sense MOS transistor 22 are turned on and the load current I_(OUT) flows, like the semiconductor device of the first embodiment. At this time, a voltage which is substantially identical with the voltage at the boundary in the P-type base region 34 and the N-type semiconductor region 32 is taken out to the node n1.

On the other hand, the sense amplifier circuit 74 controls the sense current I_(S) by carrying out a negative feedback operation in which the voltage of the node n1 and the voltage of the node n3 are made identical with each other by using a voltage drop due to the substrate resistance R_(SUB)′ with the sense current I_(S). Through this negative feedback operation, the voltage of the surface of the N-type semiconductor region 32 in the bottom of the trench filled with the voltage taking-out electrode 58 is controlled to be identical with the voltage of the node n1.

In this case, the magnitude of the sense current I_(S) which is drawn out from the node n3 is shown with the following equation (2):

I _(S) =I _(OUT) ×R _(SUB) /R _(SUB)′  (2)

where R_(SUB) is a substrate resistance on the path of the load current I_(OUT) which flows through the output MOS transistor 21, and R_(SUB)′ is a substrate resistance on the path of the sense current I_(S) flows. The equation (2) means that the sense current I_(S) which is proportional to the load current I_(OUT) can be generated. Here, either of the substrate resistances R_(SUB) and R_(SUB)′ has a fixed value determined based on the physical properties of the N⁺ substrate 31 and the N-type semiconductor region 32, and the precision of a ratio of R_(SUB)/R_(SUB)′ is high. Therefore, according to the semiconductor device of the present embodiment, the sense current I_(S) which is proportional to the load current I_(OUT) can be generated in a high precision.

For example, a case will be considered where a ratio of the number of trenches filled with the gate insulating film 40 and the gate electrode 41 in the output MOS transistor 21 and the number of trenches filled with the voltage taking-out electrode 58 is 1000:1. In this case, the ratio of the substrate resistance R_(SUB)′ to the substrate resistance R_(SUB) can be shown by the following equation (3):

R _(SUB) ′/R _(SUB)=1000  (3)

For example, when the substrate resistance R_(SUB) is 5 mΩ, the substrate resistance R_(SUB)′ is 5Ω.

When the load current I_(OUT) which flows through the output MOS transistor is 10 A, the voltage drop due to the substrate resistance R_(SUB) becomes 50 mV and the voltage of the node n1 becomes the voltage lower by 50 mV than the voltage of the back electrode 33 (the common drain electrode). As described above, the voltage of the node n3 through the negative feedback operation by the sense amplifier circuit 74 becomes lower by 50 mV than the voltage of the back electrode (the common drain electrode) in the same way. Because the substrate resistance R_(SUB)′ (that is, the resistance between the back electrode 33 and the node n3) is 5Ω, the sense current I_(S) which flows out from the sense current terminal 16 becomes 10 mA (=50 mV/5Ω). In this way, according to the configuration of the semiconductor device of the present embodiment, the sense current I_(S) which is proportional to the load current I_(OUT) can be obtained in a high precision.

When the trench in which the voltage taking-out electrode 58 is embedded is formed simultaneously (in the identical process) with the trench filled with the gate insulating film 40 and the gate electrode 41, the depths of both of the trenches becomes substantially identical, and accordingly the structure having a high similarity can be formed. This contributes to the improvement of the precision of the proportional coefficient R_(SUB)/R_(SUB)′ of the sense current I_(S) to the load current I_(OUT). In addition, the temperature difference between the substrate resistances R_(SUB) and R_(SUB)′ becomes small by arranging the voltage taking-out electrode 58 in a position in the neighborhood of the output MOS transistor 21 which is a main exothermic source and an influence of the temperature change can be restrained. This contributes to improvement of the precision by allowing the proportional coefficient R_(SUB)/R_(SUB)′ to be kept constant.

Note that the first embodiment and the fourth embodiment can be combined. FIG. 27 is a circuit block diagram showing a configuration of the semiconductor device in which the first embodiment and the fourth embodiment are combined. The output device section 14D and the control circuit section 15E are integrated on the semiconductor chip 1E. The output device section 14D has the output MOS transistor 21 and the sense MOS transistor 22, and has the structure for the electrical connection with the node n3, as mentioned above. The control circuit section 15E has the control circuit block 23, the voltage detecting circuit 24 and the sense amplifier circuit 74. The configurations of the control circuit block 23 and the voltage detecting circuit 24 are as described in the first embodiment. Also, the configuration of sense amplifier circuit 74 is as described in the fourth embodiment.

FIG. 28 is a sectional view showing the configuration of the semiconductor chip 1E. In the semiconductor chip 1E, the configuration for the electrical connection with the node n3 is added to the configuration of the semiconductor chip 1 in the first embodiment. That is, in the output device section 14D, the trench is formed to pass through the P-type base region 34 to the N-type semiconductor region 32 from the front-side main surface of the semiconductor substrate 30 and the trench is filled with the voltage taking-out electrode 58. The voltage taking-out electrode 58 is connected with the node n3. In addition, in the control circuit section 15E, the N⁺ diffusion layer 42 is formed on the surface of the N-type semiconductor region 32 and the voltage taking-out electrode 43 is joined with the N⁺ diffusion layer 42. The voltage taking-out electrode 43 is connected with the node n2.

The semiconductor device having the configuration of FIG. 27 and FIG. 28 has the functions of both of the semiconductor device of the first embodiment and the semiconductor device of the fourth embodiment. The detection signal S_(DET) is outputted to the logic circuit 25 according to the voltage between the node n1 and the node n2 (i.e. the load current I_(OUT)), and the operation of monitoring the load current I_(OUT) is carried out by the logic circuit 25. For example, the operation to detect over-current and the operation to detect the light load or no load are carried out by the logic circuit 25. In addition, the sense current I_(S) which is proportional to the load current I_(OUT) is generated in a high precision by carrying out the negative feedback operation by the sense amplifier circuit 74 to equalize the voltage of the node n1 and the voltage of the node n3.

Note that the above-mentioned embodiments and modification examples may be combined in a range of no contradiction. For example, the output MOS transistor 21 and the sense MOS transistor 22 which have the structures shown in FIG. 10, FIG. 11, and FIG. 12 in the second to fourth embodiments may be used, and also the output IGBT 21A and the sense IGBT 22A which have the structure shown in FIG. 14 may be used. The output MOS transistor 21 and the sense MOS transistor 22 which have the structure shown in FIG. 10, FIG. 11, and FIG. 12 may be used. Also, the output IGBT 21A and the sense IGBT 22A which have the structure shown in FIG. 14 may be used. Also, the output device section 14 with the structure shown in FIG. 16 and FIG. 17 in the second to fourth embodiments may be used.

<Application to in-Vehicle Electronic System>

In the in-vehicle electronic system (an electronic system installed in a vehicle such as a car) in recent years, a request of the function safety is rising and it is required to detect the state of the load in a higher precision. Therefore, it is useful to apply the above-mentioned semiconductor device which can detect the state of the load in the higher precision, to the in-vehicle electronic system. For example, in this case, as the load to be driven, a lamp for the vehicle, a fan motor, and a sheet heater are exemplified.

A case where an extraordinary event is caused in the load in the in-vehicle electronic system to which the above-mentioned semiconductor device is applied, for example, when the light load state is caused due to a broken conductive wire or an over-load state is caused due to the formation of short-circuit, the extraordinary event of the load is detected by the above-mentioned semiconductor device. The occurrence of the extraordinary event of the load is notified to the controller, more specifically, the MCU (micro controller unit). The MCU controls the above-mentioned semiconductor device in response to the notice of the occurrence of the extraordinary event of the load to turn off the output MOS transistor 21, and thereby to secure the safety. Also, the MCU notifies the occurrence of the extraordinary event to an instrument cluster (instrument panel) provided for a driver seat so that a driver can recognize the extraordinary event. Also, the MCU may notify the occurrence of the extraordinary event to the in-vehicle failure diagnosis unit so that the in-vehicle failure diagnosis unit may store the occurrence of the extraordinary event and the situation of the extraordinary event.

FIG. 29 shows the electronic control unit (ECU) 111 installed in a vehicle 110 as an example of the in-vehicle electronic system to which the semiconductor device in the above-mentioned embodiment is applied. The vehicle 110 is provided with various units actually but only the instrument cluster (the instrument panel) 112 and the in-vehicle failure diagnosis unit 113 are shown in FIG. 29.

FIG. 30 is a block diagram showing an example of the configuration of electronic control unit 111. The electronic control unit 111 of FIG. 30 is configured as a body control module. The electronic control unit 111 drives various types of loads 116 according to the operation of various types of switches 114 and the angle of a handle (a steering ring) detected by a handle angle sensor 115.

In the configuration of FIG. 30, the electronic control unit 111 includes a MCU 121, a driver IC 122 and a CAN (controller area network) transceiver 123. The MCU 121 controls the driver IC 122 to drive the load 116. The driver IC 122 drives the load 116 under the control by the MCU 121. The CAN transceiver 123 is used to carry out data communication with another equipment through a CAN 117. In the configuration of FIG. 30, the instrument cluster 112 and the in-vehicle failure diagnosis unit 113 are connected with the CAN 117. The MCU 121 of the electronic control unit 111 is possible to communicate with the instrument cluster 112 and the in-vehicle failure diagnosis unit 113. Another ECU may be connected with the CAN 117. In FIG. 30, the other ECU is referred to by reference numeral 119. The instrument cluster 112 is an equipment group used to tell the driver of the vehicle 110. The in-vehicle failure diagnosis unit 113 is a unit which is used to diagnose the failure of vehicle 110. The in-vehicle failure diagnosis unit 113 holds a log file, and when the occurrence of the extraordinary event in the vehicle 110 is notified from another equipment, the in-vehicle failure diagnosis unit 113 stores the extraordinary event log (for example, the date and time when the extraordinary event has occurred and the extraordinary contents) to the log file.

In the present embodiment, the semiconductor device (i.e. semiconductor chip 1, 1A to 1E) of the above-mentioned embodiments is used as the driver IC 122. The above-mentioned semiconductor device has a high detection precision of the load state, more specifically, the high detection precision of load current and it is desirable to use the semiconductor device as the driver IC 122 of the electronic control unit 111. For example, in case where the load 116 includes a plurality of lamps 116 a connected in parallel, a failure can be detected by detecting the load current in the high detection precision when one of the plurality of lamps 116 a is failed to an open state.

FIG. 31 is a diagram showing a connection between the MCU 121 and the driver IC 122 when the semiconductor chip 1 shown in FIG. 1 is used as the driver IC 122. The MCU 121 supplies an external control signal IN to the driver IC 122 (semiconductor chip 1) to control the ON/OFF state of the output MOS transistor 21 of the driver IC 122. On the other hand, a diagnosis terminal 29 is provided in the driver IC 122 to output the detection signal S_(DET) to the MCU 121. The MCU 121 monitors the detection signal S_(DET) and detects the extraordinary event of the load 116.

In one embodiment, the MCU 121 may carry out an operation of detecting the generation of the over-current by using detection signal S_(DET). In this case, the set threshold voltage VTH is set according to the equation (1) based on the set value I_(OUT)* which is used in case of the detection of the over-current. FIG. 32 is a flow chart showing the operation of the MCU 121 when detecting the generation of the over-current by using the detection signal S_(DET). It is supposed that in the initial state, the external control signal IN is in the high level and the output MOS transistor 21 is in the ON state. In this state, the load current I_(OUT) is supplied to the load 116.

The MCU 121 executes a detection routine at appropriate timing to detect the generation of the over-current. When the detection routine is started, the MCU 121 detects the signal level of the detection signal S_(DET) outputted from the driver IC 122 (Step S01). When the detection signal S_(DET) is in the low level, the detection routine ends just as it is.

When the detection signal S_(DET) is in the high level, i.e. the load current I_(DET) is larger than the set value I_(OUT)*, the MCU 121 sets the external control signal IN to the low level and to turn off the output MOS transistor 21 (Step S02). Thus, the supply of the load current I_(OUT) to the load 116 is stopped.

Moreover, the MCU 121 notifies the generation of the over-current to the instrument cluster 112 and the in-vehicle failure diagnosis unit 113 (Step S03). The ECU 118 of the instrument cluster 112 displays the generation of the over-current by using a predetermined equipment (e.g. a pilot lamp) which is contained in the instrument cluster 112. Also, the in-vehicle failure diagnosis unit 113 records the generation of the over-current in a log file. When the above operation completes, the execution of the detection routine ends. A service engineer who carries out the repair and check of the vehicle 110 can know that the extraordinary event such as the generation of the over-current is generated in the load 116 by checking the log file of the in-vehicle failure diagnosis unit 113.

FIG. 33 is a diagram showing a connection between the MCU 121 and the driver IC 122 when the semiconductor chip 1 shown in FIG. 9 is used as the driver IC 122. The MCU 121 supplies the external control signal IN to the driver IC 122 (semiconductor chip 1) to control the ON/OFF state of the output MOS transistor 21 of the driver IC 122. On the other hand, a diagnosis terminal 29 a to output the detection signal S_(DET1) to the MCU 121 and a diagnosis terminal 29 b to output the detection signal S_(DET2) to the MCU 121 are provided for the semiconductor chip 1. The MCU 121 monitors the detection signals S_(DET1) and S_(DET2) and detects the extraordinary event of the load 116.

In one embodiment, the MCU 121 may carry out an operation of detecting the generation of the over-current using the detection signal S_(DET1) and detecting the generation of a light load state by using the detection signal S_(DET2). In this case, the set threshold voltage V_(TH1) is set according to the equation (1) based on the set value I_(OUT1)* which is used in case of the detection of the over-current and the set threshold voltage V_(TH2) is set according to the equation (1) based on the set value I_(OUT2)* which is used in case of the detection of the light load state. Here, the following relations are established in the set values I_(OUT1)*, I_(OUT2)*:

I _(OUT2) *<I _(OUT1)*  (4)

In this case,

V _(TH2) <V _(TH1)  (5)

is met.

FIG. 34 is a flow chart showing the operation of the MCU 121 when detecting the generation of the over-current by using the detection signal S_(DET1) and detecting the generation of the light load state by using the detection signal S_(DET2). It is supposed that in the initial state, the external control signal IN is in the high level and the output MOS transistor 21 is in the ON state. In this state, the load current I_(OUT) is supplied to the load 116.

The MCU 121 executes a detection routine at appropriate timing. When the detection routine is started, the MCU 121 detects the signal level of the detection signal S_(DET2) outputted from the driver IC 122 (Step S11). When the detection signal S_(DET2) is in the low level, i.e. the load current I_(OUT) is smaller than the set value I_(OUT2)*, the MCU 121 notifies the generation of the light load state to the instrument cluster 112 and the in-vehicle failure diagnosis unit 113 (Step S12). The ECU 118 of the instrument cluster 112 displays the generation of the light load state by using a predetermined equipment (e.g. a pilot lamp) which is contained in the instrument cluster 112. Also, the in-vehicle failure diagnosis unit 113 records the generation of the light load state in the log file. After that, the detection routine advances to a step S13. Note that the detection signal S_(DET2) is in the high level, the detection routine advances to the step S13 without executing a step S12.

Moreover, the MCU 121 detects the signal level of the detection signal S_(DET1) outputted from the driver IC 122 (Step S13). The detection routine ends just as it is when the detection signal S_(DET1) is in the low level, i.e. the load current I_(OUT) is smaller than the set value I_(OUT1)*.

When the detection signal S_(DET1) is in the high level, i.e. the load current I_(OUT) is larger than the set value I_(OUT1)*, the MCU 121 sets the external control signal IN to the low level to turn off the output MOS transistor 21 (Step S14). Thus, the supply of the load current I_(OUT) to the load 116 is stopped.

Moreover, the MCU 121 notifies the generation of the over-current to the instrument cluster 112 and the in-vehicle failure diagnosis unit 113 (Step S15). The ECU 118 of the instrument cluster 112 displays the generation of the over-current by using a predetermined equipment (e.g. a pilot lamp) which is contained in the instrument cluster 112. Also, the in-vehicle failure diagnosis unit 113 records the generation of the over-current in the log file. When the above operation completes, the execution of the detection routine ends.

A service engineer who carries out the repair and check of the vehicle 110 can know the generation of the light load state and the generation of the over-current by checking the log file of the in-vehicle failure diagnosis unit 113.

FIG. 35 is a diagram showing a connection between the MCU 121 and the driver IC 122 when the semiconductor chip 1A shown in FIG. 18 is used as the driver IC 122. The MCU 121 supplies the external control signal IN to the driver IC 122 (semiconductor chip 1A) to control the ON/OFF of the output MOS transistor 21 of the driver IC 122. On the other hand, the diagnosis terminal 29 is provided for the semiconductor chip 1A to output the detection signal S_(DET) to the MCU 121. The MCU 121 monitors the detection signal S_(DET) to detect an extraordinary event of the load 116.

In the configuration of FIG. 35, the generation of over-current may be detected based on the detection signal S_(DET). In this case, the set threshold voltage VTH is set according to the equation (1) based on the set value I_(OUT)* which is used in case of the detection of the over-current. Also, the generation of the light load state may be detected based on the detection signal S_(DET). In this case, the set threshold voltage VTH is set according to the equation (1) based on the set value I_(OUT)* which is used in case of detection of the light load state.

FIG. 36 is a diagram showing a connection between the MCU 121 and the driver IC 122 when the semiconductor chip 1D shown in FIG. 24 is used as the driver IC 122. The MCU 121 supplies the external control signal IN to the driver IC 122 (semiconductor chip 1D) to control the ON/OFF state of the output MOS transistor 21 of the driver IC 122. On the other hand, the MCU 121 monitors the sense current IS which is outputted from the sense current terminal 16 of the driver IC 122. In detail, in the configuration of FIG. 36, an external resistance REX is connected between the sense current terminal 16 and the ground terminal 8, and the MCU 121 monitors the sense current I_(S) by monitoring the sense voltage V_(S) generated when the sense current I_(S) flows through the external resistance REX. The sense voltage V_(S) is a voltage corresponding to the sense current I_(S). The MCU 121 detects an extraordinary event of the load 116 from the voltage level of the sense voltage V_(S), i.e. the current level of the sense current I_(S).

In one embodiment, the MCU 121 may carry out an operation of detecting the generation of the over-current and the generation of the light load state based on the sense voltage V_(S) (i.e. the sense current I_(S)). In this case, an over-current threshold (a threshold of the sense voltage V_(S) to detect the over-current) and a light load threshold (a threshold of the sense voltage V_(S) to detect the light load) are set to the MCU 121.

FIG. 37 is a flow chart showing the operation of the MCU 121 when detecting the generation of the over-current and the generation of the light load state based on the sense voltage V_(S) (i.e. the sense current I_(S)). It is supposed that the external control signal IN is in the high level and the output MOS transistor 21 is in the ON state. In this state, the load current I_(OUT) is supplied to the load 116.

The MCU 121 executes a detection routine in appropriate timing. When the detection routine is started, the MCU 121 detects the voltage level of the sense voltage V_(S) and compares the detected sense voltage V_(S) with the light load threshold (Step S21).

When the sense voltage V_(S) is lower than the light load threshold, that is, when the load current I_(OUT) is smaller than the set value (a first set value) as a reference for determining the light load, the MCU 121 notifies the generation of the light load state to the instrument cluster 112 and the in-vehicle failure diagnosis unit 113 (Step S22). The ECU 118 of the instrument cluster 112 displays the generation of the light load state by using a predetermined equipment (e.g. a pilot lamp) which is contained in the instrument cluster 112. Also, the in-vehicle failure diagnosis unit 113 records the generation of the light load state in the log file. After that, the detection routine advances to a step S23. Note that when the sense voltage V_(S) is higher than the light load threshold, the detection routine advances to the step S23 without executing a step S22.

Moreover, the MCU 121 compares the sense voltage V_(S) with the over-current threshold (Step S23). In case where the sense voltage V_(S) is lower than the over-current threshold, i.e. the load current I_(OUT) is smaller than the set value (a second set value) as a reference for determining the over-current, the detection routine ends just as it is. Note that the set value (the second set value) as the reference for determining the over-current is greater than the set value (the first set value) as the reference for determining the light load.

In case where the sense voltage V_(S) is higher than the over-current threshold, i.e. the load current I_(OUT) is greater than the set value (the second set value) as the reference for determining the over-current, the MCU 121 sets the external control signal IN to the low level to turn off the output MOS transistor 21 (Step S24). Thus, the supply of the load current I_(OUT) to the load 116 is stopped.

Moreover, the MCU 121 notifies the generation of the over-current to the instrument cluster 112 and the in-vehicle failure diagnosis unit 113 (Step S25). The ECU 118 of the instrument cluster 112 displays the generation of the over-current by using a predetermined equipment (e.g. a pilot lamp) which is contained in the instrument cluster 112. Also, the in-vehicle failure diagnosis unit 113 records the generation of the over-current and the value of the sense voltage V_(S) in such a case (that is, a value of the sense current I_(S)) in the log file. When the above operation completes, the execution of the detection routine ends.

The service engineer who carries out the repair and check of the vehicle 110 can know the generation of the light load state and the generation of the over-current by checking the log file of the in-vehicle failure diagnosis unit 113.

FIG. 38 is a diagram showing a connection between the MCU 121 and the driver IC 122 when the semiconductor chip 1D shown in FIG. 27 is used as the driver IC 122. The MCU 121 supplies the external control signal IN to the driver IC 122 (semiconductor chip 1D) to control the ON/OFF state of the output MOS transistor 21 of the driver IC 122. The diagnosis terminal 29 to output the detection signal S_(DET) to the MCU 121 is provided in the driver IC 122 in addition to the sense current terminal 16 which outputs the sense current I_(S). The MCU 121 monitors the sense current I_(S) and the detection signal S_(DET) to detect an extraordinary event of the load 116. Here, in the configuration of FIG. 38, the external resistance REX is connected between the sense current terminal 16 and the ground terminal 8. The MCU 121 monitors the sense current I_(S) by monitoring the sense voltage V_(S) generated when the sense current I_(S) flows through the external resistance REX.

In one embodiment, the MCU 121 may carry out an operation of detecting the generation of the over-current based on the detection signal S_(DET) and detecting the generation of the light load state based on the sense voltage V_(S) (i.e. the sense current I_(S)). In this case, a light load threshold (a threshold of the sense voltage V_(S) to detect the light load state) is set to the MCU 121. Also, the MCU 121 may carry out the operation of detecting the generation of the over-current based on the sense voltage V_(S) (i.e. the sense current I_(S)) and detecting the generation of the light load state based on the detection signal S_(DET). In this case, the over-current threshold (a threshold of the sense voltage V_(S) to detect the over-current) is set to the MCU 121.

In the above, application examples of the semiconductor device of the present invention have been specifically described but it could be easily understood to the skilled person in the art that the semiconductor device of the present invention can be applied to various application fields.

The present invention has been specifically described based on the above embodiments. However, the present invention is not limited to the embodiments and various modifications can be accomplished in a range not apart from the scope of the present invention. 

What is claimed is:
 1. A driver IC (Integrated Circuit) comprising: a power supply terminal; an output terminal to be coupled to a load element; a connection node on a current path between the power supply terminal and the output terminal; a substrate resistance, having one end coupled to the connection node; an output transistor including a gate, wherein the output transistor is coupled in series with the substrate resistance through the connection node; a resistance, having one end coupled to an other end of the substrate resistance; and a voltage detecting circuit configured to detect a voltage depending on a voltage between the one end of the substrate resistance and the other end of the substrate resistance, and to output an output signal, which is as an output of the voltage detecting circuit, to the gate of the output transistor, wherein the output transistor and the voltage detecting circuit are formed in a semiconductor substrate, wherein the semiconductor substrate includes semiconductor layers, wherein the substrate resistance is coupled to the resistance through a first layer in the semiconductor layers, and wherein the substrate resistance and the output transistor are on the current path.
 2. The driver IC according to claim 1, further comprising: a sense transistor including a gate, wherein the voltage detecting circuit comprises at least an input terminal, and wherein the sense transistor is provided on a path between the input terminal and the other end of the resistance.
 3. The driver IC according to claim 1, wherein the output transistor includes a Metal Oxide Semiconductor (MOS) transistor.
 4. The driver IC according to claim 1, wherein the output transistor includes an Insulated Gate Bipolar Transistor (IGBT).
 5. The driver IC according to claim 1, wherein the other end of the substrate resistance is coupled to the power supply terminal, and wherein one terminal of the output transistor is coupled to the connection node, and an other terminal of the output transistor is coupled to the output terminal.
 6. The driver IC according to claim 1, wherein the other end of the substrate resistance is coupled to the output terminal, and wherein one terminal of the output transistor is coupled to the connection node, and an other terminal of the output transistor is coupled to the power supply terminal.
 7. The driver IC according to claim 2, further comprising: a threshold voltage generator configured to generate a threshold voltage, and wherein the threshold voltage generator is provided between the other input terminal of the voltage detecting circuit and the other end of the substrate resistance.
 8. The driver IC according to claim 1, wherein the load element includes a lamp.
 9. The driver IC according to claim 8, wherein the voltage detecting circuit is configured to detect failure of the lamp by using the voltage depending on the voltage between the one end of the substrate resistance and the other end of the substrate resistance.
 10. The driver IC according to claim 1, wherein a value of the resistance is higher than that of the substrate resistance.
 11. The driver IC according to claim 2, wherein the output transistor is formed in a first semiconductor region in the semiconductor substrate, and the sense transistor is formed in a second semiconductor region in the semiconductor substrate, and wherein the first semiconductor region is adjacent to the second semiconductor region.
 12. The driver IC according to claim 2, wherein the output transistor includes a MOS transistor, and the sense transistor includes a MOS transistor, and wherein the semiconductor substrate includes a common gate region in which the gate of the output transistor and the gate of the sense transistor are formed.
 13. The driver IC according to claim 12, wherein the output transistor is formed in a first semiconductor region in the semiconductor substrate, and the sense transistor is formed in a second semiconductor region in the semiconductor substrate, and wherein the first semiconductor region is adjacent to the second semiconductor region.
 14. The driver IC according to claim 12, wherein the output transistor is formed in a first semiconductor region in the semiconductor substrate, and the sense transistor is formed in a second semiconductor region in the semiconductor substrate, and wherein the first semiconductor region is adjacent to the second semiconductor region through the common gate region. 